The professor worked for 7 hours at a ________.
正确答案： A
本题解析：
此题考查的是固定词组搭配。 at a stretch 一口气地
Washing the food down with water as a substitute ________ chewing is not a good habit
He ________ his poor judgment ________ Jet Lag.
Police are ________ the disappearance of two children.
Each of us should _______ aside a few minutes to have a rest every day.
We were told that the stone figure _______ back to the 16th century was of great value.
Perseverance is a kind of quality and that is _______ it takes to do anything well.
You should help them ________ when your friends quarrel with each other.
We are interested in the weather because it _______ us so directly—what we wear, what we do and even how we feel.
—David has made great progress recently. — _______，and _______.