No-till farming to conserve soil fertility because
a) remnants of the previous crop are left to slowly decay
b) deep ridges are cut across, not down, the slopes of hills
c) the ground is carefully turned to mix soil nutrients
d) only organic fertilizers and natural pesticides are used

a) remnants of the previous crop are left to slowly decay

Explanation:

No-till farming also called zero tillage farming is an agriculture technique or way of growing crops without disturbing the soil through tillage.

No-till cultivation is meant to enhance the amount of water infiltrating the soil, the preservation of organic matter by the soil, and its nutrient cycling. It can reduce soil erosion in a few agricultural areas.

Here correct answer is a) remnants of the previous crop are left to slowly decay

answer; /// the above statement is (true);

real, smaller and upside-down.   so the answer should be b.