be good at 后面加动词 ing 形式。be good at意为“擅长……”，be good at后接名词、代词或动名词。at 是介词，介词后面要跟名词、代词或动名词即动词的ing形式,例如I am good at teaching English.I am good at football。 

      be good at的用法举例
      be good at后接动名词
      例句：He is good at learning Maths.他擅长学数学。
               I'm good at playing foottball. 我擅长踢足球。

       1.You have to be good at spotting trouble on the way and heading it off.

       你必须善于发现潜在的麻烦并加以化解。

       2.A teacher should be good at drawing inferences about other cases from one instance.

       老师要善于举一反三。