I won’t tell the student the answer to the math problem until he ____on it for more than an hour.
He was breathing ______ after the relay race.
People are concerned about the quality of the air they ______.
She walked home by herself, ______ she knew that it was dangerous.
—Let's go Dutch for this supper, OK? —No,________this time, as a reward for all your help.
At the United Nations Climate Change Conference, the UN Secretary General points out that,________, the climate situation will get worse and worse.