Occur against the background

牛津词典对against的解释,本题符合第5条：
1
opposing or disagreeing with somebody/something
the fight against terrorism
We're playing against the league champions next week.
We were rowing against the current.
That's against the law.
She was forced to marry against her will.
Are you for or against the death penalty?
She is against seeing (= does not want to see) him.
I'd advise you against doing that.
2
not to the advantage or favour of somebody/something
The evidence is against him.
Her age is against her.
compare for preposition (7)
3
close to,touching or hitting somebody/something
Put the piano there,against the wall.
The rain beat against the windows.
4
in order to prevent something from happening or to reduce the damage caused by something
an injection against rabies
They took precautions against fire.
Are we insured against theft?
5
with something in the background,as a contrast
His red clothes stood out clearly against the snow.
(figurative) The love story unfolds against a background of civil war.
6 used when you are comparing two things
You must weigh the benefits against the cost.
Check your receipts against the statement.
What's the rate of exchange against the dollar?