How does GNMA improve mortgage marketability?

I. GNMA sponsors pools of FHA$-$ or VA$-$insured mortgages

II$.$ GNMA provides timing insurance to investors

III.GNMA ensures the timely receipt of promised cash flows in the event of homeowner default

IV$.$ Most GNMA pools do not allow assumable mortgages

Only I & III

Only I and IV

I, II$,$ and III

I, II$,$ and IV