Terrace farming is a common agricultural practice in Sikkim due to:

The correct answer is: c) Mountainous terrain.

Terrace farming is a type of agriculture that is used in mountainous areas. It involves creating a series of terraces on the side of a hill or mountain. This allows farmers to grow crops on land that would otherwise be too steep or rocky to farm.

Sikkim is a state in India that is located in the Himalayas. It is a mountainous state with a lot of steep terrain. Terrace farming is a common agricultural practice in Sikkim because it allows farmers to grow crops on land that would otherwise be unusable.

The other options are incorrect because:

• Fertile plains are not common in Sikkim. The state is mostly mountainous, with a few small plains.
• Abundant irrigation systems are not necessary for terrace farming. The terraces collect rainwater and snowmelt, which provides enough water for the crops.
• Large-scale mechanization is not possible in terrace farming. The terraces are too small and steep for large machines to operate.