So difficult _______it to work out the problem that I decided to ask Tom for some advice
A.I did findB.did I findC.I’ve foundD.have I found在线课程B
句意：发现解决这个问题如此困难，所以我答应向汤姆咨询一下。So位于句首，应使用部分倒装。另外本句用过去时态。