They make a promise _they would help us when we had trouble选什么A what B which C thatD why
问题描述：
They make a promise _they would help us when we had trouble选什么
A what
B which
C that
D why
答
C,同位语从句
答
选C ，that 做promise的同位语。
此句翻译为，他们承诺当我们有困难的时候会帮助我们。
答
c
答
C that
这个是同位语从句，
从句中的句子什么成分都不缺，所以可以用which或that
但是，一般情况下都会用that
所以选C