Why does the effect of plant roots in a rock with fine cracks increase over time?

Correct answer: Roots thicken and continuously press crack walls

The direct answer is A: roots become thicker as they grow and keep pressing against the walls of fine cracks. Biological weathering means that living organisms help break or weaken rocks. A root may enter a small crack; as the plant grows, the root becomes longer and thicker. This creates repeated pressure, especially when water is also present, and the crack gradually widens. Option A is correct because it describes slow, continuous root pressure. Option B is wrong because roots do not instantly melt rock; melting requires very high temperature. Option C is wrong because roots do not always block water, and water can often enter the crack. Option D is wrong because roots do not make temperature constant. The process is gradual, not sudden. Memory cue: growing roots act like slow natural wedges inside cracks.