How did astronomers use technology to identify characteristics of the crab nebula? technology that detects ultraviolet light found hydrogen in the nebula technology that detects radio waves identified a pulsar at the center of the nebula technology that detects microwaves revealed the behavior of electrons in the nebula technology that detects gamma rays measured the distance of the nebula from earth

The answer is;  technology that detects radio waves identified a pulsar at the center of the nebula

The crab nebulae is as a result of a supernova event due to the collapse of a massive star. The remnants of the supernova is an outward moving cloud of gas and the center is a pulsating neutron star called a pulsar. The pulsar emits highly charged particles and radio waves. The radio waves are able to pass through the cloud nebulae as it pulsates and is detectable by a radio telescope. Other waves of higher frequency are easily blocked by the nebulae gas.

technology that detects radio waves identified a pulsar at the center of the nebula

i think its the first one