21. Other types of waste flow into our water, _______ river and sea life.
A. kill B. killing C. to kill D. killed
22 Although we produce carbon when we breathe, the carbon we produce is much less than _____ produced by a car.
A. that B. it C. one D. the one
23 The girl found the T-shirt sold online was _______that in the supermarket.
A. as half cheap as B. cheap as half as
C. the half price of D. half the price of
