额定电流为0.9A，电阻值为50Ω的电阻器能接于380V或220V的电源。（）
参考答案：错
________ astronauts cannot go to a baseball game or a movie in orbit , there are many familiar activities that they can still enjoy.
A．While
B．Since
C．Before
D．Unless
同种免疫反应是引起血小板输注无效的主要原因。（）
