20.To reduce erosion, people can .

Plant grass and shrubs. Bare soil is easily swept away by wind and water, the two main causes of erosion. Plant roots hold the soil together, while their leaves block rain and stop it breaking the soil apart.[1] X Trustworthy Source Virginia Cooperation Extension Publications and Educational resources from Virginia Tech and Virginia State University Go to source Turf, ornamental grass,  

Add mulch or rocks. This will weigh down the soil and stops the soil from moving.

Explanation:

plant cover crops or place mulch above the eroded area

option a is correct i.e.

explanation:

in context to the membrane of nerve impulse, the outer membrane of neuron is semi permeable that is only sodium ions can pass through the membrane i.e. smaller ions can pass through the membrane while larger ions cannot pass through it.