6（）

单项选择题To understand what true happiness is one must （）

A．have as much fun as possible during one"s lifetime
B．make every effort to liberate oneself from pain
C．put up with pain under all circumstances
D．be able to distinguish happiness from fun

单项选择题The best title for this passage is （）

A．Traveling in Space
B．Sleeping in the Spacecraft
C．Equipment Used by Astronauts
D．The Earth Seen from Outer Space