Smoking is one of the ______ of heart disease and it kills lots of people every year.
—Do you believe that difficult situations or hard experiences _______ the best qualities of a man?—There is no doubt about that.
—Would you mind my opening the window to let some fresh air in?—Not in the least. ________.
December 17, 2011 was a sad day for the North Koreans, ______ their top leader Kim Jung-ill passed away unexpectedly.
—You seem familiar with Mr. John?—Sure, we ______ together for three years in the 1990s.
Most students think this book is useful as it _______ all the basic grammar rules they need to know.