**Core Concept**
The highway truck driver is likely experiencing allergic rhinitis, a common condition characterized by an overactive immune response to environmental allergens, leading to symptoms such as profuse rhinorrhea (runny nose) and sneezing. This condition involves the release of histamine and other chemical mediators from mast cells, which causes blood vessels to dilate and leads to increased mucus production.

**Why the Correct Answer is Right**
Fexofenadine is a non-sedating, second-generation antihistamine that effectively blocks the action of histamine at the H1 receptor, thereby reducing the symptoms of allergic rhinitis. By inhibiting histamine's effects, fexofenadine helps to decrease nasal congestion, sneezing, and rhinorrhea. This medication is a suitable choice for a highway truck driver as it does not impair cognitive function or cause drowsiness, allowing the individual to continue driving safely.

**Why Each Wrong Option is Incorrect**
**Option A:** **Pseudoephedrine** is a decongestant that can cause vasoconstriction, reducing nasal congestion. However, it may not address the underlying allergic response and can have side effects such as increased heart rate and blood pressure.
**Option B:** **Montelukast** is a leukotriene receptor antagonist that is effective in treating allergic rhinitis. However, it is not the most suitable choice for immediate relief of symptoms like rhinorrhea and sneezing.
**Option C:** **Ipratropium bromide** is an anticholinergic medication that can help reduce nasal secretions, but it is more commonly used to treat chronic bronchitis and COPD. It is not the first-line treatment for allergic rhinitis.

**Clinical Pearl / High-Yield Fact**
When treating allergic rhinitis, it's essential to consider the individual's occupation and lifestyle. Non-sedating antihistamines like fexofenadine are often preferred over sedating antihistamines or decongestants to minimize the risk of impaired cognitive function and motor skills.

**Correct Answer:** D. Fexofenadine.