My classmate told me that the word of 'such' appeared in the bracket should be revised to 'very’, and he told me that the word of 'such' couldn't link with another adjective.

　　Yes and no. Your friend is right you cannot say "such few"... you would have to say "such a few," or "such a lot." But you can say "such beautiful flowers," where "such" modifies the adjective "beautiful." Also, "She has been in such pain lately."

　　In the example you mentioned above, I think one of the problems with using "such" there is SEMANTIC, i.e., the meaning. "Such" and "so" are used to describe the degree of something, similar to the Chinese 那么，那么多车。 That usage would not be logical or idiomatic in the above sentence.

　　Also, I can't think of any situation right now where we would say "such few"-- we would say "so few."

　　"Such" can be used as an adverb and as an adjective, but the usage rules are tricky. So much of this needs to simply be memorized.

　　ADVERB: For example, "I'm surprised that so few people came to the concert." "These are such large cookies; I can't eat a whole one."

　　ADJECTIVE: For example, "I never dreamed there would be such a wonderful audience."

　　Snakes are (capable of) graceful (motion) throughout the (entire long) of their rubbery (bodies).

　　In this example, the correction should be “throughout the entire length” …:

　　"Motion" can be a count noun AND a MASS/non-countable noun.(like "sugar," "water.") -- meaning that it can have "s" in plural form and can also be used without the plural.

　　In this case, "motion" is used to describe a QUALITY or STATE of movement. "Action" is a similar word that can be used without the "s"-- "James Bond is a man of action." Here the "action" described is quality of being, and not a series of actions he has performed.

　　An example of a sentence using "motions": “I watched the motions of the snake from a safe distance and examined the creature."

　　I found this example by doing a search on Google, and you can see that in this case, the writer is talking about discrete, countable movements and not a state of being.

　　The difference in usage is subtle, but if you pay close attention, you can learn the rules. Again, a lot of usage is simply frequent exposure and memory.