4. For each of the following use a Karnaugh map to produce the minimal product of sums. For each shade each distinguished 0-cell. Also, if more than one possible minimal

answer is possible, give the possible answers. \text { a. } \quad J a(a, b, c)=\prod(1,2,5,6) \text { b. } \quad J \mathrm{~b}(a, b, c, d)=\prod(1,3,5,7,13,15) \text { c. } \quad J c(a, b, c, d)=\prod(1,3,6,9,11,12,14) \text { d. } \quad \mathrm{Jd}(a, b, c, d)=\sum(0,1,2,5,8,10,13) \text { map in 1's but circle 0's }