**Core Concept**
The patient's presentation is highly suggestive of a ruptured abdominal aortic aneurysm (AAA), a life-threatening condition that requires prompt surgical intervention. The underlying risk factors for AAA development include atherosclerosis, family history, smoking, and hypertension.

**Why the Correct Answer is Right**
Smoking is a major risk factor for the development of AAA, as it leads to the accumulation of macrophage-derived foam cells in the aortic wall, promoting inflammation and atherosclerotic plaque formation. The patient's 40-pack-year smoking history significantly increases his risk of developing an AAA. Additionally, smoking accelerates atherosclerosis, which is a key component of AAA pathogenesis.

**Why Each Wrong Option is Incorrect**
**Option A:** While hypertension is a risk factor for atherosclerosis, it is not as directly linked to AAA development as smoking. Hypertension can contribute to the progression of AAA, but it is not the most likely risk factor in this patient.

**Option B:** Asthma is not a recognized risk factor for AAA development. While asthma can be associated with other cardiovascular conditions, such as coronary artery disease, it is not directly linked to AAA.

**Option C:** Type-2 diabetes mellitus (DM) is a risk factor for atherosclerosis and cardiovascular disease, but it is not as strongly associated with AAA development as smoking. DM can contribute to the progression of atherosclerosis, but it is not the most likely risk factor in this patient.

**Option D:** Lisinopril, an ACE inhibitor, is used to treat hypertension and is not a risk factor for AAA development. In fact, ACE inhibitors like lisinopril may even have protective effects on the aortic wall.

**Clinical Pearl / High-Yield Fact**
Smoking is the most significant risk factor for AAA development, and patients with a history of smoking should be screened for AAA, particularly if they have a family history of the condition.

**Correct Answer:** D. Smoking is the most likely risk factor to have contributed to the development of his underlying condition.