PEOPLE DON'T KNOW WHAT CAUSED THE ACCIDENT.A. IT WAS NOT KNOWN WH...

4. People don't know what caused the accident.

A. It was not known what caused the accident.

B. The cause of the accident was not known.

C. It's not known what has caused the accident.

D. It's not known what caused the accident.

II. Identify the one underlined word or phrase that must be changed for the sentence to be correct