As you make your way to the first door at location A, a soldier will inform you that you can find the β communicator inside. Sure enough, when you enter the door, you will see the green communicator in the upper left corner. Grapple over to it and collect it, and then return outside. You'll be needing this communicator for the next few areas.
A red solider with a knife is running around to the right of A, but all he can do is threaten you. As you make your way up to the ledge before door B, you may notice a red robot patrolling the area. Contact with this robot will cost you one bar of health, so be careful.
When you step inside door B, you will see a floating platform and a man in the upper right corner. If you go to the trouble to reach this person, he will simply give you fairly obvious advice in NES version: use caution. He won't tell you anything else insightful, and even tries to shoo you away in FC version.