Which of the following is a fact?

Arrange the sentences below to form a logical paragraph.an experienced rock climber knows that it takes a combination of knowledge and preparation to perform a successful climb.a successful climb begins with a proper foothold, carefully placing each foot on a ledge or crack then reaching for a solid hold, and finally pushing off.in addition to a proper foothold, a climber must be careful to check the integrity of the rock before stepping because it has to be solid clear through.a veteran climber judges the integrity of the rock and chooses not to climb on conglomerates, packed clay with lots of little rocks.but, such knowledge of rock is not the only preparation a skilled climber needs; equally important is the correct equipment.with these tools, knowledge of rock composition and equipment safety, a climber may experience many safe and enjoyable climbs.

In the sentence above, which verb is the irregular verb? a. laid b. warmed c. removed d. walked

Pls, i really need on this question?