Questions 18 to 20 are based on the following passage. At the end of the passage, you will be given 15 seconds to answer the questions. Now, listen to the passage.

The pyramids were built

A．before the Egyptians developed a sophisticated technology.
B．after the Egyptians developed a sophisticated technology.
C．to house the tombs of all ancient Egyptian kings and nobles.
D．to keep mummies safe forever.