These problems are too hard to work out, ______

下列句中加点词语发生活用的情况不同其它三项的是（ ）

Guesswhhave experienced

President Trump announced that the United States would ________ from the Paris Climate Agreement, which would possibly weaken efforts to fight global warming.

So many people are standing outside the hall. ________ will the concert begin—________ seven o’clock.