When the First Pulsar Was Discovered, Scientists Thought It Might

When the first pulsar was discovered, scientists thought it might be a signal from a distant extraterrestrial civilization. However, this idea was quickly discarded because:

A) it was realized the signals were interference from cars and trucks passing by the radio observatory
B) the government made the scientists hide their original finding
C) they realized that Cepheid variables could produce the detected radio signals
D) more pulsars were discovered, which meant that these were natural phenomena
E) the technology required to create pulsed signals is beyond the power of any civilization