副詞 as yet:

1. used in negative statement to describe a situation that has existed up to this point or up to the present time
   同義詞：so far, thus far, up to now, hitherto, heretofore, yet, til now, until now

1. The side-effects of the drug are as yet unknown (toscientists).
   這種藥的副作用(科學(xué)家)尚未發(fā)現(xiàn)。
2. As yet we haven't heard from him.
   我們到現(xiàn)在還沒有收到他的信。
3. We are as yet unable to say when the train will arrive.
   我們還說不上火車什么時候到達(dá)。
4. We should be responsible for the generation as yet unborn.
   我們應(yīng)該對下一代負(fù)責(zé)。