I have a hard time(to know/knowing)who my real friends are.

问题描述:

I have a hard time(to know/knowing)who my real friends are.

选 knowing
理由; have a hard time doing sth
解释; 我很难知道我真正的朋友是谁

答案是 knowing 翻译:我很难知道我真正的朋友是谁.
语法结构:
good / lovely
have a hard time + ( in ) doing sth.
difficult