When you drive home, you can’t be＿＿＿＿＿＿＿careful. 

Since Tom_____ downloaded a virus into his computer, he can not open the file now.

When I saw mum nod _______ to me, I calmed down and went on with my acting.

Many people think they have to spend a lot of money to keep healthy. Leading a healthy lifestyle doesn't have to cost much,         . 

 — It's so cold today.    — Yes, it's       colder than it was yesterday.