The mother was nervous because she had nother son who was away at a boarding school.A. he

问题补充：

The mother was nervous because she had nother son who was away at a boarding school.

A. heard from

B. heard of

C. heard about

D. heard out

答案：

(答案→)A. heard from

B. heard of

C. heard about

D. heard out

解析：短语辨析。A收到sb的来信；B=C听说；D听完；根据句意可知A正确。句意：那位母亲很紧张，因为她很久没有收到在住宿学生学习的儿子的来信。