In lines 13-17, why does the author compare tree roots with growing salt crystals?

A. They both force hard surfaces to crack.

B. They both grow as long as water is available.

Thông tin: Like tree roots breaking up a

sidewalk, the growing crystals exert pressure on the rock and eventually pry the rock apart

   along planes of weakness, such as banding in metamorphic rocks, bedding in sedimentary

rocks, or preexisting or incipient fractions, and along boundaries between individual

mineral crystals or grains.

Chọn A