All of the answers are right.
The bodies of water did offer opportunities for easy travel.
The location did make it easier to defend the empire.
The location did provide opportunities for trade with Europe, China, and Africa.
And the location did offer opportunities for controlling movement in and around the territory.
A. The bodies of water offered opportunities for easy travel.
- This is definitely true! Istanbul has access to two bodies of water: the Mediterranean and the Black Sea.
B. The location made it easier to defend the empire.
-Well, I am not too sure about this one: its problematic (but in total I would say false). The location allowed for a better defense of the city, but not of the whole empire, in fact soon the western part of the empire was attacked and lost: so I would say that it made it harder to defend the empire.
C. The location provided opportunities for trade with Europe, China, and Africa.
This is definitely true! it was at crossroads between Asia and Europe!
D. The location offered opportunities for controlling movement in and around the territory
- I think that this is also true! It allowed for a control of ship movement from the Black Sea to the Mediterranean and the land journey from Asia to Europe.