________,Johnhasbeentoseveralforeigncountries.
Tostudyaforeignlanguage,__________.
Whenhesuddenly________upthesubjectofgeneticengineering,therewasanembarrassedsilence.
Othersarguethatsincetheearthhasenduredalongstringoficeagesinthelasttwomilliontothreemillionyears,anywarmingis________tobetemporary.
Insomeschoolschildrenwhoprefertoreadbooksratherthan________footballbecomesocialoutcasts(被抛弃者).