For transistor action,which of the following statements is correct?

In common emitter mode of a transistor, the d.c. current gain is $20$, and the emitter current is $7 \,mA$. The collector current is (in $/ 3 \,mA$)

In a transistor, comparing the doping of emitter, base, and collector, the part which is heavily doped and that which is lightly doped are respectively:

Given below are two statements:
Statement $I:$ In a typical transistor,all three regions emitter,base and collector have same doping level.
Statement $II:$ In a transistor,collector is the thickest and base is the thinnest segment.
In the light of the above statements,choose the most appropriate answer from the options given below.

An $NPN$ transistor is used in common emitter configuration as an amplifier with $1\,k\Omega$ load resistance. $A$ signal voltage of $10\,mV$ is applied across the base-emitter. This produces a $3\,mA$ change in the collector current and $15\,\mu A$ change in the base current of the amplifier. The input resistance and voltage gain are:

For a transistor in $CE$ mode to be used as an amplifier,it must be operated in: