gy days, you have to drive very ________ on theexpressway to avoid traffic accidents.

下列文学文化常识的阐释中不正确的一项是（ ）

(2013·潍坊高考模拟)Air pollution is getting more and more serious，so we must take action________it is too late

I will meet my uncle the morning December 21st.

Here are three balls, ___?