题目

Nowadays ________ Internet is becoming increasingly popular and    new high speed broadband network was recently started.  A. a; the  B. the; a  C. a; a  D. the; the 答案： 选B。本题主要考查冠词的用法。Internet为特指对象；而一条高速的新宽带网为泛指，用不定代词a。如图30，在△ABC中，∠B=2∠C，AD⊥BC于D，M为BC的中点，AB=10厘米，则MD的长为______．