Explanation:
In TDM (Time Division Multiplexing) a) several signals are sent in a time slotted mode on a channel.

TDM (Time Division Multiplexing):
TDM is a technique used in telecommunications to transmit multiple signals over a single communication channel. It divides the time into multiple time slots, and each signal is allocated a specific time slot for transmission.

Multiple Signals:
In TDM, multiple signals are sent over the channel. These signals can be voice, data, or any other form of information that needs to be transmitted. Each signal is given a specific time slot to transmit its data.

Time Slotted Mode:
In TDM, the channel is divided into time slots, and each signal is allocated a specific time slot. The signals are sent one after the other in a sequential manner. Each signal gets a fixed amount of time to transmit its data before the next signal in line gets its turn.

Advantages of TDM:
- Efficient utilization of the channel: TDM allows multiple signals to be transmitted over a single channel, maximizing the utilization of the channel's capacity.
- Simplicity: TDM is a relatively simple technique to implement and manage.
- Cost-effective: TDM eliminates the need for multiple dedicated channels, reducing costs.

Other Options:
b) Several signals are sent on separate channels at a time - This is not correct because TDM combines multiple signals into a single channel, rather than sending them on separate channels simultaneously.
c) One signal is sent to several users - This is not correct because TDM is used to transmit multiple signals, not a single signal to multiple users.
d) None of these - This is not correct as the correct answer is option 'A'.
e) All of these - This is not correct as TDM does not send signals on separate channels simultaneously or send one signal to several users.

Therefore, the correct answer is option 'A' - Several signals are sent in a time slotted mode on a channel in TDM.