Look at the verbs.give the second and the third forms .write them into 2 columns: regular verbs and irregular verbs . список глаголов : discover , sail ,be interested (in) ,appear , prepare , smoke , depend (on) , fight , sell.

Regular verbs: discovered - discovered, sailed - sailed, appeared - appeared, prepared - prepared, smoked - smoked, depended- depended (on).
irregular verbs: was interested (in) - been interested (in), fought - fought, sold - sold.