Premise:
"While it is unclear just what the right level of saving is, it is clear that America needs to begin saving more if it is to avoid severe problems in the future."
Hypothesis: There might be a financial emergency in the future and it is a good idea for Americans to save money even though it is unclear what the right level of saving is.

it is not possible to tell

Premise:
"but uh so what what do you like why do you like David Letterman"
Hypothesis: Oh, so you're not a fan of David Letterman?

no

Premise:
"The existing emission rate limitations for individual boilers, which are based on boiler type, are not changed."
Hypothesis: Boilers have no limitations.
no