20．A well-written composition__________ a good choice of words and clear organization among other things．

　　　　 A．calls on　　　 　　 B．calls for　　　 　　 C．calls up　　 　　　　 D．calls off

19．Distinguished guests and friends, welcome to our school! _____the ceremony of the 50th anniversary this morning are our alumni (校友) from home and abroad．

　　　　 A．Attend　　　　 　 B．To attend　　　 　 C．Attending　　 　　 D．Having attended