Humanbehaviorismostlyaproductoflearning________thebehaviorofanimalsdependsmainlyoninstinct.
A、soWhenhesuddenly________upthesubjectofgeneticengineering,therewasanembarrassedsilence.
EachyearintheUnitedStates,manyblackteenagers_______ofschool,eitherbecausetheycannotkeepuportheyhavetoworktosupporttheirfamily.
Constructionoftherailwayshelpedtodevelopthenational_______ofTanzaniaandZambia.
Theboyranoutoftheclassroomwithouttheteacher's_______.
________withthesizeofthewholeearth,thehighestmountainsdonotseemhighatall.
