List of top Signals and Systems Questions on LTI systems asked in GATE EC

The outputs of four systems $(S_1, S_2, S_3, S_4)$ corresponding to the input signal $\sin(t)$, for all time $t$, are shown. Based on the given information, which of the four systems is/are definitely NOT LTI (linear and time-invariant)?
Let $x_1(t)=e^{-t}u(t)$ and $x_2(t)=u(t)-u(t-2)$. If $y(t)$ is the convolution $x_1(t)x_2(t)$, find \[ \lim_{t\to\infty} y(t) \] (rounded to one decimal place).