Arrange these structures in decreasing order of size:
a. sarcomere
b. fibril
c. filaments
d. fiber

The correct answer will be Fiber → fibril → sarcomere →  filaments.

Explanation:

Skeletal muscle is made up of long and cylindrical skeletal cell with a diameter up to 100 μm which are known as muscle fibres.

These muscle fibre encloses the smaller fibrils of 1.2 μm diameter which runs along the length of a muscle fiber.

Within each myofibril is enclosed the functional unit of muscle called sarcomere which is composed of contractile myofilaments- actin (thin filament) and myosin (thick filament).

Thus, Fiber → fibril → sarcomere →  filaments are the correct answer.