American Indians ________ about five percent of the U.S. population .
| A．fill up | B．bring up | C．make up | D．set up |
----- Must I turn off the gas after cooking?
----- Of course. You can never be ______ careful with that.
| A．enough | B．too | C．so | D．very |
He told me he had been offered a well-paid ____, but he refused it.
| A．business | B．service | C．work | D．position |
He has written a lot of books, but ______ good ones.
| A．any | B．some | C．few | D．many |
Everyone here will thank the firefighters for the things they do to prevent fires ______ the environment safer.
| A．to make | B．make | C．making | D．from making |
If Newton lived today, he would be surprised by what ______ in science and technology.
| A．had discovered | B．had been discovered |
| C．has discovered | D．has been discovered |