The correct answer is option 'C', which states that the delays caused in the switching of timing signals are due to propagation delay. Let's understand this in detail.

Propagation delay refers to the time taken for a signal to travel from the source to the destination. In the context of timing signals, it is the time taken for a signal to propagate through a wire or a circuit from one component to another. This delay is primarily caused by factors such as the distance the signal needs to travel, the properties of the medium through which it travels (e.g., wire, PCB trace), and the characteristics of the components that the signal passes through.

Now, let's break down the factors that contribute to the delays in switching timing signals:

1. Distance: The longer the distance the signal needs to travel, the greater the propagation delay. This is because the signal takes time to propagate through the medium. For example, in a large circuit board or a network of interconnected components, the signals may need to travel considerable distances, resulting in increased delays.

2. Medium: The properties of the medium through which the signal travels also affect the propagation delay. Different mediums have different propagation speeds. For instance, signals propagate slower through a wire compared to a PCB trace. The electrical properties of the medium, such as resistance, capacitance, and inductance, also influence the propagation delay.

3. Components: The components that the signal passes through, such as gates, transistors, or buffers, introduce some delay due to their internal characteristics. These delays can vary depending on the specific component and its design. For example, in digital circuits, logic gates have propagation delays associated with their switching times.

Overall, the delays caused in the switching of timing signals primarily occur due to the propagation delay, which is influenced by factors such as the distance the signal needs to travel, the properties of the medium it travels through, and the characteristics of the components it passes through. By understanding these factors, engineers can design circuits and systems to minimize propagation delays and improve overall signal timing.