1-C. I didn't immediately recognize Professor Smith at the conference yesterday.I didn't immediately recognize Professor Smith at the conference yesterday.
3-C. This was because the participants who missed the conference did not know in which time zone the company was located.This was because the participants who missed the conference did not know in which time zone the company was located.
4-C. For example, a company in Indiana once scheduled a phone conference with companies in other states.For example, a company in Indiana once scheduled a phone conference with companies in other states.