1.①a.The town was once again under attack last night.
b.She started attacking the thief with a stick.
②If you were__attacked(attack), would you be able to defend yourself？
③My new neighbor, whom I introduced to you the other day, had__a__heart__attack(心脏病发作) last night.
2.①a.Similar problems exist in other countries as well.
b.It was impossible for them to exist on such a small income.
②There exists a good way to solve the existing problem in maths.(exist)
③No one knows when such a custom first came into existence(exist).
3.①a.My deskmate claimed to__compete(compete) with me for the prize.
b.He claimed to__have__done(do) the work without help.
②It__is__claimed__that(据说) some doctors were working 80 hours a week.
