Variant 1 You could have come first and won the race if you … faster

18. The shop assistant placed the crystal vase … on the shelf.

A) careful B) carefully C) careless D) carelessly

Why do we sleep? Amazingly, that`s a question with no definite answer. We all know that we fall asleep because we are tired and that feel better after sleeping, but why can`t we do without it? Research has shown that animals die if they don`t have food. But why do we need it? The time we are asleep is divided into different periods. D-sleep (desynchronized or dreaming) and S-sleep (synchronized). A typical night`s sleep consists of four or five periods of D-sleep that lasts approximately 90 minutes total (little more than 20 per cent of total sleep time). The first D-sleep period occurs about 7 to 12 minutes after falling asleep.