Which of the Following Techniques Yields a Simple Random Sample

Which of the following techniques yields a simple random sample?

A) Choosing volunteers from an introductory psychology class to participate
B) Listing the individuals by ethnic group and choosing a proportion from within each ethnic group at random
C) Numbering all the elements of a sampling frame and then using a random number table to pick cases from the table
D) Randomly selecting schools, and then sampling everyone within the school