数字卫星通信系统的关键传输质量指标是（）。

A.信噪比

B.输入电平

C.比特差错率

D.输出电平

1)______Noam Chomsky
2)______D. A. Wilkins
3)______Piaget
4)______Hymes
5)______Stephen Krashen
a) cognitive theory of learning
b) communicative competence
e) Transformational Generative Linguistics
d) the monitor hypothesis
e) function-notion syllabus design