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The professor could hardly find sufficient grounds _____his arguments in favor of the new theory.

A. to be based on     B. to base on   

C. which to base on    D. on which to base

The professor could hardly find sufficient grounds _____his arguments in favor of the new theory.

A. to be based on     B. to base on   

C. which to base on    D. on which to base

The professor could hardly find sufficient grounds _____his arguments in favor of the new theory.

The professor could hardly find sufficient grounds _____his arguments in favor of the new theory.

A．to be based on     B．to base on         C．which to base on    D．on which to base

The professor could hardly find sufficient grounds _____his arguments in favor of the new

theory.