They are all very clever, but _______of them could work the problem out.

— Which of the caps will you take?—I’ll take______ , one for my father, the other for my mother.

The price system is a complex network composed of the prices of all the products bought and sold in the economy as well as       of a great number of services. 

The nutrients in _____falls into the ocean quickly become available to other living creatures.

—Shall I attend my friend's coming­of­age ceremony, Mum?—No, unless you see to ________ that you will be home before 1000 PM.