Some of the students are not sure ___ spelling the word, while others are not sure ___ the use of some grammatical rules.
We set off _______ the Three Gorges _______ a beautiful afternoon from Fu Ling.
He missed _______ gold in the high jump, but will get _______ second chance in the long jump.
Sorry to say it will be years _______ we really have classes here with only 25 students.
--Why are you so depressed, Lily? --- I lost the contest narrowly, or I _________ the award of $10,000.
Hurricane Sandy struck the northeastern United States, ____________ millions of people homeless.