I just don't understand_______ that prevents so many Americans from being as happy as one might expect.
| A．why it does | B．what it does | C．what it is | D．why it is |
—I wonder what makes you a successful manager.
—I ________ as a waiter for five years，which contributes a lot to my today’s work.
| A．serve | B．have served |
| C．had served | D．served |
The traffic rule says young children under the age of four and ________ less than 40 pounds must be in a child safety seat.
| A．being weighed | B．to weigh |
| C．weighed | D．weighing |
—What do you think of the 2013 Spring Festival Party?
—Well，great！But I don’t think much of ________ held last year.
| A．the one | B．it |
| C．one | D．which |
Due to the widespread ________ of this medical technology，more diseases can be discovered and treated at an early stage.
| A．presentation | B．application |
| C．qualification | D．appreciation |
—________ one and a half months enough for the project to be finished?
—I am afraid not.The professor is ill and only after he recovers ________ go on with it.
| A．Is；he can | B．Are；he can |
| C．Is；can he | D．Are；can he |