For each value of d.f. look up the value of Student's t in Appendix D for the

Question:

For each value of d.f. look up the value of Student's t in Appendix D for the stated level of confidence. How close is the t-value to the corresponding z-value (at the bottom of the column for d.f. = ∞) ?
a. d.f. = 40, 95 percent confidence
b. d.f. = 80, 95 percent confidence
c. d.f. = 100, 95 percent confidence