Select the most appropriate option that can substitute the highlighted segment in the given sentence to improve it. If no improvement is required, select ‘No improvement required’.
The pollution level ought to keep under control.

Correct option is A

The correct substitution of the highlighted words is (a) "ought to be kept."
· The sentence is in the passive voice, indicating that the action (keeping the pollution level under control) should be done by someone. Therefore, the correct phrase is "ought to be kept," which properly conveys that the pollution level needs to be maintained by an unspecified subject.
· Grammatical rule used: In passive voice constructions, "ought to" is followed by "be" + past participle to indicate that the action should be done by someone or something.
· Example: "The rules ought to be followed strictly."
Explanation of incorrect options:
· Option (b) ought to have kept : Incorrect because it implies a past action that should have been completed, which doesn’t fit the intended meaning of ongoing control.
· Option (c) No improvement required : Incorrect because the original sentence lacks the correct passive construction.
· Option (d) ought to be keeping : Incorrect because this phrase suggests a continuous action, which is not appropriate for the intended meaning of maintaining control over time.