Consider the two regular expressions

$R_1=a^{**}|b^{**}{R}_2|=a{b}^{**}|b{a}^{**}|b^{**}a|(a^{**}b{)}^{**}|$

i$)$ Find a string corresponding to $R_1$ but not to $R_2.$

ii$)$ Find a string corresponding to $R_2$ but not to $R_1.$

iii$)$ Find a string corresponding to both $R_1$ and $R_2.$

iv$)$ Find a string corresponding to neither $R_1$ nor $R_2.$