Please explain

2. For each set of carbocations, circle the one that is most stable (lowest energy). Remember, when comparing conjugated cations, you must examine the resonance contributors or resonance hybrids. CH3 CH3 (CH-C-CH-CH) CH3-CH-CH=CH2 CH3 CH-CH-CH2-CH a) CH3 CH3 1 CH3-C-CH2-CH3 CH3 CH3-C=CH-CH2 = CH3-CH-c-CH3 CH3 b) CH3 CH3-C-CH=CH2 * CH3 CH=C-CH-CH3 c) CH3 BrC-CH2-CH3 CH3 CH3-C=CH-CH CH3 CH3 CH3 -CH-CH2-CH i CH3 CH3 CH3-C=CH-CH-CH3 - CH3 CH3-CH-C-CH3 NO2 d) CH3 1+ Br-C-CH=CH-CH3 CHCH2 !! CH3-C-C-CH3 NO 2 e)