People around the country were excited the astronauts came back to the earth safely.A. u

问题补充：

People around the country were excited the astronauts came back to the earth safely.

A. unless

B. but

C. until

D. because

答案：

A. unless

B. but

C. until

(答案→)D. because

解析：考查连词。A. unless除非； B. but但是；C. until直到；D. because因为。句意：全国各地的人们都很激动，因为宇航员安全地返回地球。故D正确。