1)

Investors usually knows that short term US treasury bills pay the lowest yields, then short-term corporate paper pays more, then treasury bonds pays more, then long-term corporate bonds pay the most.

Using technical terminology explain Why is that must be true ?

2)

Market interest rates dropped to the lowest levels seen since the 1950s at the beginning of the great recession.

Using technical terminology how this can be explained? What happened to the demand for financing and what would have been happening with inflation?