Give examples of languages $\mathrm{L}_1$ and $\mathrm{L}_2$ over $\{a, b\}$ that satisfy the descriptions below.
a) $\mathrm{L}_1$ is regular, $\mathrm{L}_2$ is nonregular, and $\mathrm{L}_1 \cup \mathrm{L}_2$ is regular.
b) $\mathrm{L}_1$ is regular, $\mathrm{L}_2$ is nonregular, and $\mathrm{L}_1 \cup \mathrm{L}_2$ is nonregular.
c) $L_1$ is regular, $L_2$ is nonregular, and $L_1 \cap L_2$ is regular.
d) $\mathrm{L}_1$ is nonregular, $\mathrm{L}_2$ is nonregular, and $\mathrm{L}_1 \cup \mathrm{L}_2$ is regular.
e) $L_1$ is nonregular and $L_1^*$ is regular.