1.A new theory ______ before it can be put into practice.
A.must be tested B.should be tested
C.can be tested D.to be tested
2.This is the house _____ windows were broken.
A.whose B.which C.its D.of which
3.New machinery _____ arriving tomorrow.
A.will be B.is C.are D.shall be
4.Eliza is really an expert in dancing,but ____singing her performance is anything but good.
A.as long as B.when it comes to
C.as far as D.as long as
5.What ____ it is to swim in such hot weather!
A.a fun B.fun C .funny D.interesting

1.选A.must be tested 意思是选理论用于实践前必须得到检验。
答案B.should be tested 从语法上讲也不错。但口气没有答案A强。因为一般来说，理论一定要选检验后才能用于实际，而不只是应该，否则会出现大乱子的。
楼上的选D显然是错误的。因为如果选D语句将不成句子（没有谓语）
2.A.这是一个定语从句 。此题正确答案是A，不能选择D。选择 of which 时应在名词前加上定冠词 the，也就是说如果名词前有 the 就只能用 of which。如果名词前没有冠词，就用 whose。如上句题改为：This is the house _____ the windows were broken.或 This is the house the windows _____ were broken.此题就只能选择答案D而不能选择A了。
要提醒的是 whose 可以指人，又可以指物，而 of which 只能用来指物。
3. 选A ，用将来进行时表示明天的正要发生的事
4. 选B when it comes to 当提到...，其它答案意思不适合，用法也不对（因为是连词，不能与动名词连用）
5. 选B 是感叹句 如果选C .funny D.interesting ，what就要改成 how,表示玩得开心一般用 fun.所以A答案也不太恰当。