do not remove grass!

signs like this appear all over coastal regions. why?
a) the grass holds moisture in the ground.
b) the grass provides shelter for many animals.
c) the grass to keep the sand dunes in place.
d) the grass to keep the air temperature constant.

It's C

Explanation:

The grass helps to keep the sand dunes in place. The roots of the grasses spread out to anchor the plants and the same roots help keep the sand in place. The beach grass is stopping erosion by wind.

a gas, having a molecular weight of 13 kg/kmol and a kinematic viscosity of 0.25 cm2/s, flows through a pipe 0.25 m internal diameter and 5 km long at the rate of 0.4 m3/s and is delivered at atmospheric pressure.