Write below each of the integrals, whether they are improper or proper and explain why they are improper (e.g., infinite discontinuity or infinite interval).

a) ∫[0 to [infinity]] e^(-x) dx
b) ∫[-[infinity] to [infinity]] 1/x dx
c) ∫[0 to 1] 1/√x dx
d) ∫[1 to [infinity]] ln(x) dx