Give IUPAC name of the compound

(a) 1, 1, 5-Trimethylcyclohex-5-ene

(b) 1, 3, 3-Trimethylcyclohex-1-ene

(c) 1, 1, 3-Trimethylcyclohex-2-ene

(d) 2, 6, 6-Trimethylcyclohex-1-ene