The correct answer is (a) Pinus.

Pinus is a genus of coniferous trees and is commonly known as pine trees. The largest sperms are found in the genus Pinus.

Here are some key points about the sperms in Pinus:

- The sperms of Pinus are among the largest in the plant kingdom, measuring up to 4-5 millimeters in length.
- The sperms of Pinus are flagellated, which means they have a whip-like tail that helps them to swim through the female reproductive tract to reach the egg.
- The large size of the sperms in Pinus is thought to be an adaptation to increase the chances of fertilization in wind-pollinated plants, where the sperm has to travel a long distance to reach the egg.
- The sperms of Pinus are produced in the male cones, which are smaller and less conspicuous than the female cones. The male cones release pollen grains that contain the sperms, which are then carried by the wind to the female cones.
- The female cones of Pinus are larger and more visible than the male cones. They contain ovules, which are the female reproductive structures that produce the eggs. The sperms of Pinus have to swim through a liquid droplet to reach the ovules and fertilize the eggs.

In conclusion, the largest sperms are found in the genus Pinus, which is a group of coniferous trees. The large size of the sperms is an adaptation to increase the chances of fertilization in wind-pollinated plants.