What motivated Clarence King to investigate the alleged diamond site?
A
He knew Arnold and Slack personally.
B
He needed to protect his reputation.
He enjoyed exploring the Sierra Desert.
He had been paid to help pull off the hoax.

When King learned of a spectacular diamond field in Colorado, he grew concerned because his recent study of that area gave no indication that gemstones might occur there. He visited the site and discovered that it had been salted with second-rate uncut stones. He immediately exposed the fraud.

the answer is "began" because it is a action that can be done