Part A is grammatically incorrect.

• The error is related to the auxiliary verb "which".
• "Which" is used for non-living things only.
  E.g. :- I didn't know for certain which train to take.
• But, here, we need a possessive pronoun and the correct pronoun will be "whose".
  
• It is the possessive form of "who".
  E.g. :- Juliet wondered whose the sports car was.

• In order to make the sentence correct, replace "which" with "whose".
  
• Thus, the correct sentence will be: The boy whose money was lost felt sorry.

Part C is grammatically incorrect.

• The difference between few and a few is explained below:
  
  Few = not very many, with a focus on the fact that this number is (remarkably) small.
  
  "I have few friends" implies that you have a very small set of friends (as opposed to many). In some contexts (not always!), it can also imply that you don't feel very well about it, that you wish you had more friends.
  
  It is usually used in a negative context.
  
  A few = not very many, but at least more than one
  
  "I have a few friends" is just the same as saying "I have some friends".
  
  It is usually used in a positive context. 
  
  
• Here, the possibility of a patient's recovery is been mentioned. It gives a positive sense. Thus, we will use 'a few' to show that. 
  
  The correct sentence will be: The doctor says that the patient will recover in a few days.

By checking option A:

Given expression is-

15 ÷3 + 6 × 8 – 7 = 6 + 49 ÷8 × 3 + 12

After interchanging-

15 ÷6 + 3 × 8 – 7 = 3 + 49 ÷8 × 6 + 12

After Solving,

15 ÷6 + 3 × 8 – 7 = 3 + 49 ÷8 × 6 + 12

As, 15 is not perfectly divisible 6, so it will result in decimal.

Therefore, it's not the correct option.

By checking option B:

Given expression is-

15 ÷3 + 6 × 8 – 7 = 6 + 49 ÷8 × 3 + 12

After interchanging-

15 ÷3 + 6 × 7 – 8 = 6 + 49 ÷7 × 3 + 12

After Solving,

15 ÷3 + 6 × 7 – 8 = 6 + 49 ÷7 × 3 + 12

Or, 5 + 42 – 8 = 6 + 7 × 3 + 12

Or, 5 + 42 – 8 = 6 + 21 + 12

Or, 47 – 8 = 27 + 12

Or, 39 = 27 + 12

So, 39 = 39
As, we found the correct answer, so no need to check more options.

Hence, option B is the correct answer.

After carefully observing the figures given in the question, it is very clear that the answer figure (C) will be the missing figure.

Logic- figure B is the mirror image of figure A, similarly, figure D is the mirror image of figure C.

Hence, option C is the correct answer.

Candidates who qualified for bank H =

= 210

Candidates who qualified for bank L =

= 336

Therefore, required ratio = 210 : 336

= 5 : 8

Therefore, option D is the right answer.

Let the cost price for A is 100x.

∴ According to the question,

x = 5 × 2 = 10

So, Required price = 10 × 100 = Rs.1000

* GDP is calculated on two basis-

1. On current prices called nominal GDP.

2. On Base year prices called real GDP.

* Real GDP is expressed in foundation year prices and is referred to as a fixed cost price.

* Real GDP is considered a true indicator of economic growth as it is free from currency fluctuations.

* It is also referred to as ‘GDP inflation adjusted’.

* Nominal GDP of India for the year 2020-21 is $3.05 trillion.

• The 1938 Haripura session of congress was presided by Subash Chandra Bose. 

• National Planning Committee was constituted in this session.

• Next year after the 1939 Tripuri session crisis, SC Bose resigned, and Rajendra Prasad was replaced as president.

दिए गए विकल्पों में ग्वाला का स्त्रीलिंग रूप 'ग्वालिन' है अतः सही विकल्प ‘ग्वालिन’ है। अन्य शेष विकल्प असंगत हैं।
पुल्लिंग – स्त्रीलिंग
ग्वाला – ग्वालिन
अन्य तथ्य - 
लिंग - "संज्ञा के जिस रूप से व्यक्ति या वस्तु की नर या मादा जाति का बोध हो, उसे व्याकरण में 'लिंग' कहते है।
पुल्लिंग - जिन संज्ञा शब्दों से पुरूष जाति का बोध होता है, उसे पुलिंग कहते है।
जैसे- राजा, घोड़ा, बन्दर
स्त्रीलिंग - जिस संज्ञा शब्द से स्त्री जाति का बोध होता है, उसे स्त्रीलिंग कहते है।
जैसे- माता, रानी, घोड़ी

शाखा' एकवचन शब्द है जिसका बहुवचन बहुवचन शाखाएँ होता है।
एकवचन - बहुवचन 
शाखा - शाखाएँ
वचन - जिन शब्दों से संज्ञा या सर्वनाम के एक या अनेक होने का बोध होता है, उन्हें वचन कहते हैं।
वचन दो प्रकार के होते हैं – 1.एकवचन 2.बहुवचन
एकवचन - शब्द के जिस रूप से वस्तु या व्यक्ति का एक संख्या होने का बोध हो, एकवचन कहलाते हैं।
बहुवचन - शब्द के जिस रूप से वस्तु या व्यक्ति का एक से अधिक संख्या होने का बोध हो, बहुवचन कहलाते हैं।