Crop and gizzard are characteristic features of:
The gizzard is a part of the digestive tract of birds and some reptiles. It often contains stones and pebbles which aid to ground up the ingested food. The crop is another organ of the alimentary canal of birds that stores food before digestion. Hence, these organs are found in Struthio and not in Balaenoptera, Draco, and Hippocampus.
So, the correct answer is option D.