听力原文：Hello, this message is for Jonathan Hasbrow. This is Cindy Hertz calling from Sol

听力原文： Hello, this message is for Jonathan Hasbrow. This is Cindy Hertz calling from Solid Security Inc. We will be installing a new security system in the building. On Tuesday we'll begin by replacing the video cameras for 3 days. Due to security concerns only the main entrance can be used for entering and exiting the building. All staff members are required to wear their identification passes at all times. There will be power disruptions, so it is recommended that all computers be protected as well as any experiments postponed until the changes are complete. I will be sending someone from Solid Security Inc. on Monday to address any concerns or requests you may have concerning the security installations. Thank you and have a good day.

What is being replaced？

A．The computer systems

B．The security office

C．Security cameras

D．The wireless Internet