改错：His mother isn't good at sing English songs.
问题描述：
改错：His mother isn't good at sing English songs.
答
be good at doing sth
所以sing应改为singing
答
His mother isn't good at singing English songs.
理由：be good at +doing sth 做某事在行的意思，擅于
希望对你有帮助。
答
His mother isn't good at singing English songs.
答
singing