Basicity $\mathrm{\alpha }+\mathrm{I}$ effect

Methyl group of methylamine has $+\mathrm{I}$ effect

So, methylamine is more basic than ammonia.

Similarly, the ethyl group of ethyl amine has $+\mathrm{I}$ effect and $+\mathrm{I}$ effect of ethyl is greater than that of methyl. That's why ethylamine is more basic than methylamine.

Amines can form hydrogen bonds due to the presence of high electronegative element nitrogen.

Due to the presence of hydrogen bonds in ethylamine, it has more boiling point than propane. Hence, option (D) is correct.