(49./A plane electromagnetic wave is given by E. (+ ey) exp{i(kz-ot)}. At a given location, the number of times E vanishes in one second is (a) An integer near- when 8 = nt and zero when 8 n, n is integer T (b) An integer near- and is independent of 8 TC (0) when 8 = n and zero - (c) An integer near 2 when 8 nt, n is integer (d) An integer near- @ 2 and is independent of 8