肯定句用as well、also、
否定句和疑問句用yet
例句：
We should stick to the principles and be flexible as well. 既要有原則性， 也要有靈活性。
My girlfriend was also called Helen. 我的女朋友也叫海倫。
I haven’t asked him yet. 我還沒有問他。
Has Edmund arrived yet? 埃德蒙到了嗎？