Linear time invariance RLC Why is a combination of R, L, C linear time-invariant system? But not diode, or transistor?

I looked over V-I equation for R, L, C, but still don't know how to prove it.
actually, the diode and transistor are also time-invariant components.  the transistor is even reasonably linear in a range of operation between cutoff and saturation.  even, for very small displacements, a diode can be sorta linear, but a diode in normal use is clearly not linear.