They are very grateful us them so much help.A. to to giveB. of to giveC. for giveD. t

问题补充：

They are very grateful us them so much help.

A. to, to give

B. of, to give

C. for, give

D. to, for giving

答案：

A. to, to give

B. of, to give

C. for, give

(答案→)D. to, for giving

解析：to到，向；for为了，对于。句意：因为给了他们如此多的帮助，他们对我们非常感激。结合语境可知前一空用介词to表示感激的对象，后一空有介词for表示感激的原因，故选D。