Crab salad

We need : About 20 sticks of crab 250 grams of shrimps Green onions 2 cans of sweet corn Slices of crab for decoration 1 cup green olives sliced For dressing we need : 2 tablespoons mustard 2 tablespoons lemon juice Salt and pepper 1/2cup oil 2 tablespoons of mayo (optional) 2 tablespoons of balsamic vinegar or apple vinegar