"答案A
此题考察连词的用法.
第一空what引导表语从句,what在表语从句中作表语.
第二空when引导定语从句,先行词是20 years ago.本题较难.What引导表语从句,what在从句中作主语、宾语或表语;that也可引导表语从句,但不作成分,不能省略且无词义.
①Is this what you want to tell me?(what引导表语从句,同时又作tell的宾语)
②The problem is that we have not enough money to buy the expensive car.(that引导表语从句,但不作成分)"