$A$ transistor works as an amplifier when

In the case of $NPN$ transistors,the collector current is always less than the emitter current because:

For a transistor in the active region:
$(a)$ Base,emitter,and collector regions should have similar size and doping concentrations.
$(b)$ The base region must be very thin and lightly doped.
$(c)$ The emitter-base junction is forward-biased and the base-collector junction is reverse-biased.
$(d)$ Both the emitter-base junction and the base-collector junction are forward-biased.
Which one of the following pairs of statements is correct?

In an $n-p-n$ transistor,$200$ electrons enter the emitter in $10^{-8} \ s$. If $1 \%$ of electrons are lost in the base,then the current that enters the emitter and the current amplification factor are respectively $\left[e=1.6 \times 10^{-19} \ C\right]$

$A$ common emitter transistor amplifier is connected with a load resistance of $6 k\Omega$. When a small a.c. signal of $15 mV$ is added to the base-emitter voltage, the alternating base current is $20 \mu A$ and the alternating collector current is $1.8 mA$. What is the voltage gain of the amplifier?

Which two of the following statements are true for a transistor?
$(1)$ The base,emitter,and collector regions of a transistor have the same size and doping concentration.
$(2)$ The base region is thin and lightly doped.
$(3)$ The emitter-base junction is forward-biased,and the base-collector junction is reverse-biased.
$(4)$ Both the emitter-base junction and the base-collector junction are forward-biased.