Realizing that everything she said had no effect on her son, __________.

A．her son’s teacher was asked to help solve the problem.

B．it was decided that her son’s teacher should help solve the problem.

C．She had to ask her son’s teacher to help solve the problem

D．there’s nothing she can do but ask her son’s teacher to help solve the problem.

对煤工业分析的目的，是为了判断煤的（）

A．碳的含量

B．硫的含量

C．燃烧特性