1. he come late, give him the message.
2. Non-fat dairy products supply the needed nutrients without calories.
3. Although our boss had been so unkind to us, we heaped coals of fire on his by helping him in his misfortune.
4. The plumb line is always perpendicular the horizontal plane.
5. I was looking fro the magazine the whole of yesterday morning. I forgot it to you.
B. Having returned
C. To return
D. To have returned
1. 【B】虚拟语气。Should he come late相当于if he should come late,条件状语从句是虚拟的情况下，主句可用祈使语气；但是，祈使语气不可以与had done的条件状语从句连用，所以不选A；选项C,D不符合语法。故只有B 正确。
2. 【A】excessive: much more than is reasonable or necessary
Optional: if something is optional, you do not have to do it or use it, but you can choose to if you want to
Additional: more than what was agreed or expected
Arbitrary: based on personal opinion or impulse, not on reason
3. 【D】heap coals of fire on sb’s head 是固定搭配，表示“以德报怨；化干戈为玉帛”。
4. 【D】be perpendicular to sth.是固定搭配，表示“与……成直角，与……垂直”。
5. 【B】forget to do sth. “忘了去做某事” forget doing sth. “忘记做过某事”。根据题意选B。