be needed to do=be needed in order to do这个不定式是目的状语如：A lot of time is needed to do this work.(为了）做这项工作，需要很多时间。=A lot of time is needed in order to do this work.need to be done=need doing需要被做如：The watch needs repairing=The watch needs to be repaired.但如果有执行者，就只能用to be done如：The watch needs to be repaired by ...
sth/sb be needed to do sth需要某人或某物来做什么事比如 A knif is needed to kill this dog. 杀狗要用这把刀，强调的是主体在做事情中的必不可少的地位。be needed to do 的用法可以类似于be used to do(被用于)need to be done是指要做某事m...
