Scientists photographed for the first time ever _____ wild gorillas used a stick to test the depth of a pool before getting into it, according to a recent study.
In crowded places like airports and railway stations, you __________ take care of your luggage.
The teacher __________ have thought Johnson was worth it or she wouldn’t have wasted time on him, I suppose.
The weather turned out to be fine yesterday. I __________ the trouble to carry my umbrella with me.
You know he is not going to let us leave early if we __________ get the work done.
—Is Jack on duty today?—It __________ be him. It’s his turn tomorrow.