What Was the Basic Problem with the Miller-Urey Early Atmosphere

Multiple Choice

What was the basic problem with the Miller-Urey early atmosphere experiments?

A) there was no lightning on the early Earth
B) there was no hydrogen gas in Earth's early atmosphere
C) they used oxygen gas which was not present in Earth's early atmosphere
D) the mixture of gases they used was not representative of Earth's early atmosphere
E) more than one of these is correct