$x(t)$ is nonzero only for $T_x<t<{T}'x$ , and similarly, $y(t)$ is non zero only for $T_y<t<{T}'y$. Let $z(t)$  be convolution of $x(t)$ and $y(t).$ Which one of the following statements is TRUE?
1. $z(t)$ can be nonzero over an unbounded interval.
2. $z(t)$ is nonzero for $t<(T_x+T_y)$
3. $z(t)$ is zero outside of $T_x+T_y<t<{T}'_x+{T}'_y$
4. $z(t)$ is nonzero for $t>{T}'_x+{T}'_y$