Two astronauts are performing a spacewalk outside the International Space Station. If one astronaut shouts loudly, why can the other not hear them without using a radio?
a) Sound travels too slowly in space to be heard.
b) The vacuum of space lacks a medium (matter) to transmit sound waves.
c) The astronauts' suits absorb 100% of the sound energy.
d) Sound becomes "ultrasonic" in space and is inaudible to humans.