____paragraph is a group of sentences about some related subject. Readers must know what the main idea of ___paragaph is in order to understand ___information they are reading.

A．The ,a ,the

B．A,the ,the

C．A,a the

D．The ,the ,the

1970年，（）率先拉制出1000dB/km的光纤，成为世界上公认的第一根通信用光导纤维。

A.飞利浦公司；

B.朗讯公司；

C.康宁公司；

D.富士通。