______ smoking, he would not have got cancer in the lung.
| A．Was he given up | B．Had he given up |
| C．Did he give | D．If he gave up |
The first few years in the 21st century ______ the rapid rise of China as a world economic power.
| A．witness | B．has witnessed | C．will witness | D．have witnessed |
Visitors to the National Museum can avoid long lines at the ticket booths by purchasing tickets ____.
| A．in advance | B．in detail | C．out of order | D．with caution |
She told me that she would not go with us if it ____ the next day.
| A．was raining | B．rains | C．rained | D．had rained |
I know one of the things I was unsure about was _____ hard it would be to climb this mountain.
| A．what | B．that | C．however | D．how |
Some researchers are finding that daydreaming may be important to ______ mental health and it is ______ good means of relaxation.
| A．the; 不填 | B．不填 ; the | C．不填; a | D．不填; 不填 |