**Answer:**

**D) **

**Step-by-step explanation:**

A linear relationship is of the form , where, is the slope and is the y-intercept (constant).

For a **proportional relationship, the value of ** and thus it is of the form

Let us check each option and express it in the form above.

**Option A:
**

This can be written as . So, .

Since, b \ne 0, therefore, it is **not** a proportional relationship.

**Option B:
**

Here, . So, .

Since, b \ne 0, therefore, it is **not** a proportional relationship.

**Option C:
**

Here, . So, .

Since, b \ne 0, therefore, it is **not** a proportional relationship.

**Option D:
**

This can be rewritten as

There is no y-intercept on this. So,

Since,, therefore,** it is a proportional relationship.
**

Therefore, the **correct option is D.**