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.

 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.

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.

1. A.
   insure; do
2. B.
   ensure; make
3. C.
   uncertain; try
4. D.
   unsure; touch