The correct answer is option 'D': All of these.

The Harappan Civilization, also known as the Indus Valley Civilization, was one of the earliest urban civilizations in the world. It flourished in the Bronze Age (2600-1900 BCE) in the region that is now modern-day Pakistan and northwest India. The civilization was characterized by its advanced urban planning, sophisticated drainage system, and the presence of citadels and lower towns.

Urban Planning:
- The Harappan cities were meticulously planned and designed with a grid-like pattern. Streets were laid out in a grid system, dividing the cities into rectangular blocks.
- The cities were organized into different sectors, each having specific functions such as residential, commercial, and administrative areas.
- The buildings were made of brick and were multi-storied, indicating a well-developed construction technique.
- The cities were fortified with massive walls, suggesting the need for defense.

Drainage System:
- One of the most remarkable features of the Harappan Civilization was its advanced and efficient drainage system.
- Each house had its own private bathroom and toilet, with a sophisticated underground drainage system that connected to the main sewer system.
- The drainage system was carefully designed to prevent flooding and maintain cleanliness in the cities.
- The well-planned drainage system indicates a high level of urban sophistication and concern for public health.

Citadel and Lower Town:
- The Harappan cities were divided into two main parts: the citadel and the lower town.
- The citadel was a raised area within the city, often located on the western side, and was home to important public and religious buildings.
- The citadel was fortified with thick walls and had structures like the Great Bath, granaries, and possibly the residences of the ruling elite.
- The lower town was located outside the citadel and was the residential and commercial area where the majority of the population lived.
- The lower town consisted of well-planned streets, houses, markets, and workshops.

In conclusion, the Harappan Civilization was characterized by its advanced urban planning, sophisticated drainage system, and the presence of citadels and lower towns. These features reflect the high level of organization, engineering skills, and social complexity of the Harappan people.