2-Methyl propyl bromide reacts with C2H5O- and gives 'A' whereas on reaction with C2H5OH it gives 'B'. The mechanism followed in these reactions and the products 'A' and 'B' respectively are
(1) SN2. A iso-butyl ethyl ether; SN1, B = tert- butyl ethyl ether
(2) SN1, A = tert-butyl ethyl ether; SN1, B = 2- butyl ethyl ether
(3) SN1, A tert-butyl ethyl ether; SN2, B = iso- butyl ethyl ether
(4) SN2, A = 2-butyl ethyl ether; SN2, B = iso- butyl ethyl ether