It’s the fourth time that heavy smog has hit the city this month.— It’s high time we _______ measures to fight airpollution.

Could you do me a favor to hand out thesepapers—

______ his work in physics, he spent much time working for human rights and _____.

It was the first time in my life _______ I had experienced the UK

Do you know the reason _________ pilots turn off the plane’s lights before taking off? —The practice is for the passengers to adjust to the dark _________ an emergency.