Directions: In this question, a sentence has been given with some of its part in bold. To make the sentence grammatically and idiomatically correct you have to replace the bold part with the correct alternative given below. If the sentence is correct as it is, mark 'No correction required' as your answer.
» Explain it
C
More than one related instances of the past perfect tense makes the sentence ambiguous or unclear. Option A can be eliminated here. 

Option B is eliminated as well because the usage of past form with the past perfect tense is ungrammatical. 

Option D is grammatically incorrect as usage of the present perfect tense in the sentence is absurd. 

Clearly, option C is the correct answer.

 
2
The planet's average surface temperature has risen about 2.0 degrees Fahrenheit since the late 19th century, a change driving largely by increased carbon dioxide and other human-made emissions into the atmosphere.
» Explain it
B
'Driving largely by' is an incorrect form of the verb here and it should be replaced by the respective phrasal verb.

'Driven by' means providing the power to keep something working, or to make something happen.

'Driven by' is the correct phrasal verb that should be used here in this context.
Therefore, option B is the correct answer.
 
3
The serene lush green slope of the hill station make it up ideal venue for the meditation camp.
» Explain it
B
The subject mentioned in the sentence is singular and the verb used is plural form, so the incorrect part must be replaced by ‘makes it’.

‘Make someone up’ is a different phrasal verb and it is not the case here.

The article ‘an’ would be used here because of the vowel sound of 'I' in the word Ideal.

Clearly, option B is the correct answer.
 
4
By building dams across rivers, which create ponds and eventually change the rivers into wetlands, beavers help species to flourishing that would otherwise struggle.
» Explain it
A
According to grammar rule, the base form of the verb 'flourish' must be used with the infinitive 'to'. 

Ex. She likes to swim.

Options other than option A don't have the base form of the verb. Hence, they are incorrect.

Option A is the right answer.
 
» Explain it
C
The adverb 'mostly' which refers to 'Usually' or 'Generally' is wrongly used here and should be replaced by 'most' which refers to 'to the greatest extent' to make the sentence grammtically correct. All other parts which are in bold are correct and need no improvement.

Option C is hence the correct answer.