If we say L ⊂ {a, b, c}* then is L an infinite language?
$L$ is not necessarily an infinite language. $\{a,b,c\}^*$ is an infinite language, but you've written $L\subset\{a,b,c\}^*$, and infinite sets can (and do) have finite subsets. Consider $L=\{a\}$, then $L\subset\{a,b,c\}^*$ but $\lvert L\rvert=1&lt;\infty$