D[c + h, {{x, y}}, NonConstants -> {c, h}]
D[a + h, {{x, y}}, NonConstants -> {a, h}]

{D[c, x, NonConstants -> {c, h}] + D[h, x, NonConstants -> {c, h}], D[c, y, NonConstants -> {c, h}] + D[h, y, NonConstants -> {c, h}]}
{0,0}