C. Clay soil has a higher porosity than sandy soil.
Explanation:
Maller soil particles have smaller pore spaces, but a greater number of them, which leads to higher surface tension and high % porosity.
I'm thinking A. Because uniformitarianism means the theory that changes in the earth's crust during geological history have resulted from the action of continuous and uniform processes.
Answer: I and II only
Explanation:
Cover crops are planted in order to protect the soil when the main cash crop is not being planted which means that they are not planted to be harvested and can be planted after the cash crop is harvested.
The two main purposes of cash crops are to protect the soil from erosion and to improve soil fertility. Their presence reduces surface runoff of soil when it rains and slows down rain before it hits the ground at force and splits soil.
Some cover crops are planted to improve soil fertility because they improve the level of nutrients in the soil and they can also be ploughed before they mature causing them to decay and add organic matter to the soil.
Substinence farming is farming food that is just enough to live off of. You don't sell substinence crops.
Commercial farming is growing food to sustain you, and having enough left over to sell.
In both, you grow food and you keep some (or all) for yourself.
