Which of the following statements about market efficiency is true?

a) A market can be semi-strong-form and strong-form efficient but not weak- form efficient.

b) A market can be semi-strong-form efficient but not weak-form efficient.

c) A market can be semi-strong-form, weak-form or strong-form efficient but not

all simultaneously.

d) A market must be weak-form efficient if it is semi-strong-form efficient.