The correct answer is option 1, Wheat. A plant with a fibrous root system has roots that spread out in a dense network, with no single main taproot. Wheat is an example of a plant with a fibrous root system. Fibrous root systems are common in monocot plants, such as grasses and grains like wheat.

Option 2, Pea, is incorrect because peas have a taproot system, where there is a main root that grows deep into the soil.

Option 3, Mustard, is incorrect because mustard also has a taproot system.

Option 4, Bean, is incorrect because beans have a combination of a taproot and fibrous root system, with a main taproot and smaller lateral roots.

Overall, the plant with a fibrous root system is wheat, not the other three options.