ANS:D - all (a), (b) and (c)

Vibrations in the tubes of a shell and tube heat exchanger can be induced due to various factors, including:

1. Flow of fluid on the tube and shell sides: Turbulent flow or high fluid velocities can cause vibrations in the tubes as the fluid flows past them. This can result in fluid-induced vibration or flow-induced vibration.
2. Oscillations in the flow of shell/tube sides fluid: Unsteady flow conditions, such as pulsating flow or flow instabilities, can lead to oscillations in the fluid flow. These oscillations can transmit energy to the tubes, inducing vibrations.
3. Vibrations transmitted through piping and/or supports due to external reasons: Vibrations from external sources, such as nearby machinery, equipment, or environmental factors, can be transmitted through the piping and support structures to the heat exchanger tubes, causing them to vibrate.

Therefore, the correct answer is all (a), (b), and (c). Vibrations in shell and tube heat exchangers can be induced by the flow of fluid, oscillations in fluid flow, and external sources of vibration. These vibrations can potentially lead to issues such as fatigue failure, tube wear, or reduced heat transfer efficiency, highlighting the importance of proper design and maintenance to mitigate vibration problems.