单选题
Although most universities in the United States are on a semester system which offers classes in the fall and spring, some schools______ a quarter system comprised of fall, winter, and summer quarters.(2004年西南财经大学考博试题)
【正确答案】
D
【答案解析】解析：本题中，D项“observe遵守”符合题意，如：observe a rule(遵守规则)。其他三项“manipulate操作，利用；stipulate规定，保证：regulate管制，调节”都不正确。