For Venetians, flooding is nothing new.　They have long been experiencing it on a regular basis.　However, a _(21)_ flood in 1966 drew attention to a serious problem—this city is sinking at a much faster rate than previously thought.　　      In the past, Venice sank by less than one centimeter every century.　In the 20th century, however, the city has fallen by surprising 25 centimeters, which has _(22)_ far more floods than before.　 _(23)_ to just a few floods a year two centuries ago, the fact that Venice saw a hundred floods in the 20th century is very worrying.　Two factors have _(24)_ this phenomenon—rapid sinking has caused about half of the 25-centimeter drop, and the rising sea levels have been responsible for the remaining half.　The latter are a cause for greater concern.　 _(25)_the excessive amount of carbon dioxide and other gases in the atmosphere causes global warming, the polar ice caps have been melting and the oceans rising at an alarming rate.　Scientists have claimed that if this situation continues to worsen, Venice will no longer be around by the beginning of the22nd century.
【題組】21.
(A) immoral　
(B) massive　
(C) radiant　
(D) moderate