Explanation:

- The word "Dense" is an adjective used to describe the word "Crowd". A dense crowd refers to a crowd where people are closely packed together.

- Similarly, we must find an adjective that suitably describes the word "Slope".

- Option 1: Plain – This doesn't describe a slope. A plain is a flat area.

- Option 2: Tight – This doesn't describe a slope. It’s more about restrictions or constraints.

- Option 3: Fill – This isn’t an adjective and doesn’t describe a slope.

- Option 4: Steep – This is an adjective that describes a slope. A steep slope is one that rises or falls sharply.