For transistor action, state which statements are true:
(1) Base, emitter and collector regions should have similar size and doping concentrations.
(2) The base region must be very thin and lightly doped.
(3) The emitter-base junction is forward biased and base-collector junction is reverse biased
(4) Both the emitter-base junction as well as the base-collector junction are forward biased

The key to the fabrication of a transistor is to make the middle layer, the base, as thin as possible without shorting the outside layers. Statements (2) and (3) are true. The base region must be very thin and lightly doped to allow for efficient current flow from the emitter to the collector. Additionally, the emitter-base junction needs to be forward biased to inject electrons into the base, and the base-collector junction needs to be reverse biased to collect those electrons. If both junctions were forward biased (statement 4), the transistor would not function correctly. Similarly, statement (1) is incorrect because the different regions have different doping levels and sizes to achieve the necessary current flow.