_____ you can understand how the human body woks, you need to have some knowledge of chemistry
--- What’s wrong with my son, doctor? --- ____________ serious, just a slight cold. He’d better drink some water.
We have to finish so much work within two days. We can’t __________ to waste any time.
It’s the _______ that caused the big forest fire. A young man dropped it carelessly at picnic.
--- Good news, Edward has won 5 million pounds in last week’s lottery. ---How exciting! ________________________.
--- Look, what a heavy rain! What shall we do now? --- ____________ it’s raining hard, let’s stay at home to surf on the Internet.