How do you know when to use the t-distribution or when to use the z-distribution?

A) If you have a large sample size, use the t-distribution, if the sample size is small, use the z-distribution
B) If x-bar is close to mu, then use the z-distribution, if it's not, use the t-distribution
C) If you know the population standard deviation, use the z-distribution, but if you only have the sample standard deviation use the t-distribution
D) If you are unsure of the distribution shape, use the z-distribution, otherwise, use the t-distribution