When you look at this graph, you will find that it is actually the same as a mathematical curve, so you should learn to look at the trend.

You see the team in the village first:

From the origin to n and R-T are increasing.

It decreases from N-R

Other lines also have the same view.

At point n of option B, the center of the village is decreasing, while the periphery of the village is increasing.

Before point P, the homestead in the whole village is increasing, and it is positive at point P, and negative after point P, that is, it begins to decrease. So it is the largest at point P.

When you look at this curve, you need to pay attention to it. Above the x axis, it means positive, which means increasing, even a little.

When the D option reaches the R point, the waste soil in the village is not the most serious, but the waste soil has the highest speed. You should pay attention to the positive and negative values, which are negative between P and T, so no matter how much you reduce, you are reducing. In this way, the most serious time should be at point T.