In the general relation among total, marginal and average quantities, which of them are necessarily true, or which are not?
a. When the total function is rising, marginal function is rising?
b. When the total function is rising, marginal function is positive?
c. When the total function is rising, marginal function lies above it ?
d. When marginal function is rising, average function is also rising?
e. When the average function is falling, the marginal function lies below it?
f. When marginal function is neither falling nor rising, average function is constant?