Answer:
B
Step-by-step explanation:
Transistors are small pieces of semiconductor electronic devices that are used basically for amplification and switching of signals.
They are used to amplify a small signal to a larger one.
They function as switches as they determine if current flows through the collector emitter path. When a voltage is applied to the base it allows currents to flow through to C-E path, but if no current is applied no current will flow .
In the illustration given in the question the pump provides a steady flow of water when a small quantity of water is fed into it. This can be compared to the use of transistors as an amplifier in converting small signals into large signals.