vishalwin wrote:Why option B is wrong?

Option B creates a sentence that does not really make sense. The sentence almost seems to convey that the reason the powers were awarded was so that the Central Intelligence would have powers to withhold from the public - in other words something along the lines of The supreme court awarded the Central Intelligence Agency powers for it to withhold from the public.

In option A how VERB-ing is right, I mean I have seen (,VERB-ing) as correct choice when we need to show cause-effect for simultaneous actions) but not (VERB-ing without comma before).

Verb-ing modifiers, or participles, can be used in a variety of ways.

One way is to modify an entire clause. When a participle is used this way, the convention is to use a comma between the participle and the clause it modifies.

Another way a participle, or verb-ing modifier, can be used is to modify a noun. When a participle is used this way, often the participle is placed next to the noun it modifies with no comma between the noun and the participle. This structure is what you are seeing in choice A, in which powers is modified by enabling it to...