**Core Concept:**
The question is about the cause of breast sagging, which is primarily due to the weakening and stretching of the **pectoralis major** and **pectoralis minor muscles** that support the breasts. The breast tissue is composed of glandular and fatty components, and its support is mainly provided by the surrounding musculature.

**Why the Correct Answer is Right:**
In this case, the **pectoralis major and minor muscles** are stretched, leading to the sagging of the breasts. These muscles, located beneath the breast tissue, provide support and maintain the breast's shape. When stretched, the breasts lose their firmness and start to droop.

**Why Each Wrong Option is Incorrect:**
A. **Pectoralis minor muscle:** Although the pectoralis minor muscle also contributes to breast support, it is not the primary reason for breast sagging. The correct answer focuses on the pectoralis major muscle.
B. **Glandular tissue:** While the glandular tissue is responsible for breast development, it does not cause breast sagging directly. The stretching of the surrounding musculature is the primary cause.
C. **Fat tissue:** Fat tissue provides volume to the breast but does not directly cause sagging unless it is significantly reduced or removed during a procedure like reduction mammoplasty.
D. **Lower chest wall ligament:** This structure is not responsible for breast support but rather connects the breast to the ribcage.

**Clinical Pearl:**
Understanding the anatomy of the breast and its supporting structures is crucial for preoperative evaluation and informed decision-making in cosmetic breast surgery. Informed consent discussions should address the potential for breast sagging following procedures like augmentation mammoplasty or reduction mammoplasty.