D where 为正确选项.
the question occurred to me =I didn't know...where we were to get the machines needed,的 意思是“我们到哪里去找到需要的机器.”这是前置的同位语从句,正常的语序是The question where we were to get the machines needed occurred to me.where we were to get the machines needed 是question 的同位语.