题目

No one knew where my grandfather was, and many came to _____us in searching for him.   A. help       B. assist      C. provide      D. encourage 答案：B 解析: 本题从动词的搭配关系的角度可知答案为B。assist sb in doing sth帮助某人做某事。help sb (to) do sth; provide sb with sth; encourage sb to do sth。敞口放置的氢氧化钠溶液发生部分变质，除去变质生成的Na2CO3可以选择适量的（ ）A. Ca(OH)2溶液 B. 稀盐酸 C. CaCl2溶液 D. Ca(NO3)2溶液