问题
When you are _______ about which button to press on the complicated machine, you can either read the user’s guide for guidance or fax us for specific instruction. Don’t ______ the trial-and-error method.[ ]
A: insure; do
B: ensure; make
C: uncertain; try
D: unsure; touch
B: ensure; make
C: uncertain; try
D: unsure; touch
正确答案是：
