Question

Jeff asked his students, “Do you know it is important to protect the earth?” (改为间接引语)

Jeff asked his students________they ________it is important to protect the earth.

Answer

if/whether knew

【解析】

句意：杰夫问他的学生：“你们知道保护地球很重要吗？” 杰夫问他的学生他们是否知道保护地球很重要。

根据题干可知，要求改为间接引语，原句“Do you know it is important to protect the earth?”是一般疑问句，宾语从句的连词用if/whether，主句asked是一般过去时，宾语从句的时态由一般现在时变成一般过去时，know的过去式为knew；故答案为（1）if/whether（2）knew。