Choose the appropriate regular expression for the following grammar:

$SaS|bS|Q_0$

$Q_{0}d{Q}_0|c{Q}_1|$

$Q_{1}c{Q}_1|Q_2|$

$Q_{2}a{Q}_2|c{Q}_2|$

No such regular expression exists; this is not an s$-$grammar.

$(ab{)}^{**}{d}^{**}{c}^{**}(a+c{)}^{**}$

$(a+b{)}^{**}{d}^{**}c{c}^{**}(a+c{)}^{**}$

$(a+b{)}^{**}c(d+c{)}^{**}(a+c{)}^{**}$