单项选择题
One cannot learn a foreign language well（）he studies hard.
A.unless B.if C.as D.when
单项选择题 One and a half hour（）since we arrive. No one has come to meet us.
单项选择题 On my left（）a wide river; on my right, a dark forest.
单项选择题 On formal（）, people pay more attention to manners.
