Among the factors involved in building a confidence interval are:the sample size n, the level of confidence, and the margin of error. Which of the following statements are true?

a	For a specified confidence level, larger samples provide smaller margins of error.
b	For a given confidence level, a sample 16 times as large will make a margin of error one-fourth as big.
c	For a given sample size, a higher confidence level means a smaller margin of error.
d	Both a and b are true.
e	Both b and c are true.