英语完形填空（求解释选择或像老师一样讲解原文）
5　　Big schoolbags have been a serious problem for students for a long time.Maybe your schoolbag is too 41 to carry,and it troubles you a lot 42 you want to find a book out to read,Now an e-textbook will 43 you.It is said that e-textbooks are going to be 44 in Chinese middle schools.An e-textbook,in fact,is a small 45 for students.It is much 46 than a usual schoolbag and easy to carry.Though it is as small as a book,it can 47 all the materials (材料) for study.The students can read the text page by page on the 48 ,take notes with the pointer (屏写笔).Or even " 49 "their homework to their teachers by sending e-mails.All they have to do is to press a button.Some people say e-textbooks are good.but some say they may be 50 for the students' eyes.What do you think of it?
( )41.A.light B.heavy C.useful D.comfortable　
　( )42.A.till B.after C.before D.when　
　( )43.A.trouble B.prevent C.help D.understand　
　( )44.A.used B.kept C.invented D.lent　
　( )45.A.TV B.radio C.pen D.computer　　
( )46.A.heavier B.lighter C.cheaper D.brighter　　
( )47.A.hold B.build C.discover D.practise　　
( )48.A.blackboard B.desk C.screen D.card　　
( )49.A.find out B.hand in C.get back D.give back　
　( )50.A.helpful B.famous C.good D.Bad