A big security concern with Ethernet being a broadcast network is that:

Question $38$ options:

the MAC addresses are not encrypted. It is too easy to tell who sent a frame and who received that frame.

the frames become corrupted too easily, causing misinformation.

there are too many frames on the network. This can cause a denial of service.

there are too many collisions between frames. This can cause a denial of service.

there is no authentication. You don't really know who is sending a frame.