Trees are useful to man mainly in three ways, the most important of which is that they can protect ______ from droughts (干旱) and floods.
| A．it | B．itself | C．himself | D．him |
Danny left word with my secretary _______ he would call again in the afternoon.
| A．who | B．that | C．as | D．which |
Elephants have their own way to tell the shape of an object and _______ it is rough or smooth.
| A．/ | B．whether | C．how | D．what |
—Why does she always ask you for help?
—There is no one else _______, is there?
| A．who to turn to | B．she can turn to |
| C．for whom to turn | D．for her to turn |
Do you have any idea _______ is actually going on in the classroom?
| A．that | B．what | C．as | D．which |
Mary wrote an article on _______ the team had failed to win the game.
| A．why | B．what | C．who | D．that |