Which of these contributed to the decline of the roman empire?

political corruption and increasing wealth
cultural decline and military defeats
internal rebellions and uncertain leadership
increasing supplies of gold and declining roads

It is the second one. 

Caesar became politically corrupt, which led Brutus to kill him.

It could be any of those but the best answer is the second one.

the hyksos invasion. the hyksos were able to attack egypt successfully because of their skills in using bronze weapons, composite bows and the use of the horse and chariot during the invasion. although the egyptians depict a barbarian-type overthrow, the truth is the seizure was likely a relatively peaceful one.