Which sentence has a compound subject?

A fax machine has a sensor that reads the paper you are sending.
Without inventions like telephone lines and satellite transmissions, communication would be much more challenging.
Telephones, fax machines, and electronic mail transmit messages at many businesses.
A laser printer can receive a fax transmission, and a computer printer can receive one, too.

Question

Which sentence has a compound subject?

 	
	A fax machine has a sensor that reads the paper you are sending.
Without inventions like telephone lines and satellite transmissions, communication would be much more challenging.
	Telephones, fax machines, and electronic mail transmit messages at many businesses.
	A laser printer can receive a fax transmission, and a computer printer can receive one, too.