．_________life began on the earth is one of the biggest puzzles to scientists.
| A．How | B．What | C．Where | D．That |
The teacher asked us ________ in our reports before class.
| A．hand | B．to hands | C．handed | D．to hand |
Tom was the first ________ he was wrong.
| A．admit | B．to admit | C．of admitting | D．for admitting[ |
—Send me an email when you are free, will you?
—________.
| A．I must | B．I will | C．I can | D．I should |
Many students are ________ chatting online, which wastes them plenty of time.
| A．crazy about | B．connected with | C．worried about | D．anxious about |
The crowd ________ eastward, believing that they can find gold there.
| A．are headed | B．is headed | C．heads | D．are heading |