Grape: 1:3
Cherry: 5:12
Lemon: 7:12
Orange: 2:3
Multiply grape and orange by 4 to get them to include 12:
Grape: 4:12
Orange: 8:12
Now we have 4 numbers: 4, 5, 7, 8, where the second ratio is the same, so we ignore it and just look at the first part of the ratio. The smallest is 4, grape, so the answer is A.