Why is this considered to be a very limited security measure?

Access control is often implemented through the use of MAC address filtering on wireless Access Points. Why is this considered to be a very limited security measure?

A.
Vendors MAC address assignment is published on the Internet.

B.
The MAC address is not a real random number.

C.
The MAC address is broadcasted and can be captured by a sniffer.

D.
The MAC address is used properly only on Macintosh computers.