Adjective/adverb--Please help

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1)Which is correct and why:
a)the rose smells sweetly.
b)the rose smells sweet.

2)Which is correct and why:
a)The sun shines brightly.
b)The sun shines bright.

1)
b.
for verbs of perception (seems, smells, looks, feels, etc.), you use adjectives, not adverbs.
choice (a) would imply that the rose itself has an olfactory sense (and a good one, at that).

2)
a.
for action verbs, you use adverbs.

Thanks for the reply sir.
But how can we make sure that a verb has been used as an action verb or a linking verb.Consider this:
The smart man acts quickly.(manhattan SC guide,pg 73,chapter on modifiers).
Here acts is an action verb.But in
Engineers act childish when they are busy.(pg 37,Q4,English grammar,Schaum outline series,2nd edition)
act is a linking verb.
Is the following sentence correct.
The smart man acts quick.

It is a good question, though to be honest my guess is that it goes beyond the scope of what would reasonably be tested on the GMAT. But I'll give it a shot:

Generally the difference between an adjective and an adverb is that an adj answers the question "what?" and an adverb answers the question "how?" (or when, where, etc.) "Engineers act childish" is probably acceptable. In this case, you are depicting WHAT engineers act AS (They act as children, or they act childish). Alternatively, if you wanted to depict the manner in which they act, you would say "Engineers act childishly". That is HOW they act. Either is OK. The same cannot be said for the man acting quickly. This can only mean that the manner in which he acts is quick (so, use the adverb, quickly). It would not make sense to say that "quick" is a description of WHAT he acts as (a quick man? but that seems weird).

This is my best answer without further research. But again, I think it is further than you need to go for the GMAT.