Concept:
Communication is the process through which information is transmitted from one person to another.
The basic communication model consists of:
\[
\text{Source} \rightarrow \text{Encoder} \rightarrow \text{Channel} \rightarrow \text{Receiver}
\]
Step 1: Identify the Source.
Communication begins with the sender or source who creates the message.
\[
\boxed{(d) \text{ Source}}
\]
Step 2: Identify the Encoder.
The message is converted into symbols, words, gestures or signals by the encoder.
\[
\boxed{(b) \text{ Encoder}}
\]
Step 3: Identify the Channel.
The encoded message travels through a medium called the channel.
Examples:
• Telephone
• Email
• Letter
• Speech
\[
\boxed{(c) \text{ Channel}}
\]
Step 4: Identify the Receiver.
The final destination of the message is the receiver.
\[
\boxed{(a) \text{ Receiver}}
\]
Step 5: Arrange the complete sequence.
\[
(d) \rightarrow (b) \rightarrow (c) \rightarrow (a)
\]
Therefore,
\[
\boxed{\text{Option (D)}}
\]