thanghnvn Wrote:I never see "as when" in grammar book. please, explain this phrase. how to use it?
A bit of unsolicited advice: You'd be best served by spending less time reading grammar books, and more time reading normal, well-written professional English (of the sort found in, say, top newspapers or business journals).
You post this phrase often ("not found in grammar book"), and, basically every time, it's in reference to a phrase that's extremely common in written English.
You can put "as" in front of prep + noun if you're citing prep + noun as a situation in which something occurs, or is found, or whatever.
E.g.,
In football, athletes do not have to run continuously for up to 45 minutes as in soccer; in fact, they never have to run for more than about ten seconds at a time.On the GMAT, as on most standardized tests, there is no partial credit for incorrect answers.