Most birds find it safe to sleep in the trees, but they have eggs or young chicks, they don’t use a nest.[ ]

______ you got to know I traveled to the USA——Through one of your colleagues.

Since several years ago， many supermarkets in China have _______ free plastic (塑料的) bags.

Didn’t you find the film exciting?—_____, I nearly fell asleep half way through it!

Doctors Without Boarders, ________ international organization, received ________ Nobel Prize for Peace in 1999 for its outstanding work .