I think this problem is much more difficult than that one,______

She _____ on this essay for twenty minutes but she has written only about a hundred words

There is no doubt _____ man will continue to explore the vast universe in the future, but the rate at which we approach depends on the development of technology.[ ]

The boy is old enough to ________ the difference ________ right and wrong.

Finnish President said Finland-Chinarelations had progressed_______ with fruitful co-operation in new and high-techfields.