—Sorry，Mum, I lost my key to the bicycle again． —Oh! How_____ you be so careless! You have to learn to look after your belongings．

Jenny ____ have kept her word.I wondered why she changed her mind.

If the dog hadn’t woken us, we wouldn’t have noticed the fire and it _______ to the house next door．

Doctors say that exercise is important for health, but it _______ be regular exercise. 

—“What courses are you going to take next semester if you want to receive enough credits to get your degree?”—“I don’t know. But it’s about time      on something.”