**Core Concept**
An atherosclerotic plaque becomes complicated when it undergoes a process called ulceration or erosion, leading to the formation of a fibrous cap and the presence of a lipid-rich core. This transformation results in the release of pro-inflammatory molecules and the activation of various cellular pathways, ultimately contributing to plaque instability and increased risk of rupture.

**Why the Correct Answer is Right**
The correct answer features are indicative of a complicated atherosclerotic plaque due to the presence of a **ruptured fibrous cap** and **lipid-rich core**. This combination leads to the exposure of highly thrombogenic substances, such as tissue factor and phospholipids, to the bloodstream, promoting the initiation of coagulation and thrombus formation. The **infiltration of macrophages** and the **release of pro-inflammatory cytokines** further exacerbate the inflammatory response, contributing to plaque instability and increased risk of rupture.

**Why Each Wrong Option is Incorrect**
* **Option A:** The presence of a single lipid-rich core does not necessarily indicate a complicated lesion, as it can be a feature of early atherosclerosis.
* **Option B:** The absence of a fibrous cap is a characteristic of a vulnerable plaque, but it is not a feature that indicates the presence of a complicated lesion.
* **Option D:** The presence of calcification is a feature of advanced atherosclerosis, but it does not necessarily indicate a complicated lesion.

**Clinical Pearl / High-Yield Fact**
It is essential to recognize that the presence of a complicated atherosclerotic plaque is a critical risk factor for acute coronary syndromes, including myocardial infarction and unstable angina. The identification of these features in imaging studies, such as coronary angiography or intravascular ultrasound, can guide therapeutic decisions and improve patient outcomes.

**Correct Answer:** C.