be動(dòng)詞只用于這幾種情況
1）后面是doing,be doing是現(xiàn)在時(shí)的構(gòu)成
如：He () reading English.is
2）后面是done,而且的確表示被動(dòng)意思,be done是被動(dòng)語(yǔ)態(tài)的構(gòu)成
但后面是done,如不表示被動(dòng)意思,也可能是have done,完成時(shí)的構(gòu)成,這點(diǎn)要注意
如：The bike () repaired by my father last night.was 被動(dòng),被修好
My father () repaired my bike.has 完成時(shí),已經(jīng)修好
3）后面是形容詞、介賓短語(yǔ),構(gòu)成系表結(jié)構(gòu)
如：She () beautiful/short.is
I () in Class Two.am
填寫(xiě)情態(tài)動(dòng)詞,后面的動(dòng)詞必須是動(dòng)詞原形才可以考慮,有各種動(dòng)詞變形（如：doing現(xiàn)在分詞/done過(guò)去分詞/did過(guò)去式）都不能前面用情態(tài)動(dòng)詞,另外還要根據(jù)句意填寫(xiě)合適的情態(tài)動(dòng)詞：
如：He () finish the homework by today or he () submit it tomorrow.
must 必須 can't 不能
You () know I am wholehearted to you.
should / may 前面表示“應(yīng)該”,后面表示“可能”
具體要多做練習(xí),并多分析多吸取教訓(xùn),學(xué)會(huì)舉一反三