_____ to nuclear radiation, even for a short time, may produce variants (变异体) of genes in human bodies.
---Why can you speak English so fluently? ---Oh, I________ English in Shanghai International Studies University for four years.
The boy failed in the last exam, but if he continued being addicted to computer games, then so much______.
The Great Wall winds its way from west to east, _______ deserts, _______mountains and ________valleys, until at last it reaches the sea.
---I prefer spending much time solving the problem to consulting my teacher. ---That’s_______ I don’t agree. You should turn to your teacher for help if necessary.
______ relation between China and Russia has developed steadily since Vladimir Putin was re-elected______ president.