Explanation:

- Option 1: Marseille

- Marseille is a major city in France, known for its port and Mediterranean location. It has several war cemeteries but is not the location of the Heliopolis Commonwealth War Grave Cemetery.

- Option 2: Washington D.C.

- The capital city of the United States, Washington D.C., hosts numerous historic sites and memorials, including Arlington National Cemetery. However, it is not where the Heliopolis Commonwealth War Grave Cemetery is located.

- Option 3: Cairo

- Correct Answer: Cairo, the capital of Egypt, is home to the Heliopolis Commonwealth War Grave Cemetery. This cemetery commemorates Commonwealth soldiers who served in the region.

- Option 4: Athens

- Athens, the capital of Greece, contains several historical sites and cemeteries, but it is not the location of the Heliopolis Commonwealth War Grave Cemetery.