Answer:
The options are
it was too old to be used in modern times
it was too complicated for scientists to understand
scientists found new evidence to prove it invalid
scientists discovered a shorter theory to replace it
The answer is scientists found new evidence to prove it invalid
Steady State Theory of origin of the universe has been rejected due to new findings about how the universe was formed through carefully observing it which faulted past theories. This validates the option which states that scientists found new evidence to prove it invalid.