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.
Effective measures should ________ and laws should _______ to protect pandas. Otherwise, they are certain to die out.
The tree over there is so tall that I suppose it _______ nearly twenty metres.
On arrival, the famous movie star found himself _______ by the enthusiastic fans.
Modern science has given clear evidence ________ smoking can lead to many diseases.
When the news came ________ the war broke out, he decided to serve in the army.