"hubs:
a) usually incorporate repeaters or amplifiers
b) allow for simultaneous communication for all of the computers connected to them
c) limit the distance of a network to a few meters in length
d) are a difficult method to connect network cables
e) operate at the application layer"

Hubs incorporate amplifiers and repeaters.

Explanation:

Hub is an outdated way of connecting ethernet devices, they incorporate amplifiers and repeaters, they do not allow simultaneous communication among connected devices.

The latest technology in connecting ethernet devices are with the use of switch.