Currently 94%of Web users use either Internet Explorer or Firefox．but recently somenew (71) have been developed that are beginning to attract attention．The browser Opera isbecoming very (72) because of its speed，it is currently the world’S fastest browsec andbecause it is much smaller (73) existing browsers(it can almost fit on a single diskette)．It canalso (74) the last web page you visited，so the next time you surf,you can start where you leftoff．And like the big two，you can get it for free；the catch is that you have to watch blinkingads in one comeL orpay$40 forthe ad—free (75) ofOpera．

A．version
B．revision
C．software D book

当太阳风暴到达地球时，地球上具有可降低太阳活动对其影响的保护层是（   ）     

①水圈    ②大气圈         ③岩石圈     ④地球磁场

A．①②

B．①③

C．①④

D．②④