A feature of mammals without any exception is

Options

A. Seven cervical vertebrae
B. Diaphragm
C. Vivipary
D. Warm blooded nature

Answer

To determine a feature of mammals that is universally applicable without exception, we can analyze the given options step by step:

### Step 1: Analyze Option A - 7 Cervical Vertebrae
- Most mammals have seven cervical vertebrae, but there are exceptions. For instance, manatees and sloths have different numbers of cervical vertebrae. Therefore, this feature cannot be considered universal for all mammals.

**Hint:** Consider whether the feature is present in every single mammal or if there are exceptions.

### Step 2: Analyze Option B - Diaphragm
- The diaphragm is a muscular structure that separates the thoracic cavity from the abdominal cavity and is responsible for the breathing process. All mammals possess a diaphragm, making this feature universal among them.

**Hint:** Look for a feature that is essential for a specific function and is found in all members of the group.

### Step 3: Analyze Option C - Viviparity
- Viviparity refers to giving birth to live young rather than laying eggs. While most mammals are viviparous, the platypus (Ornithorhynchus) is an exception as it lays eggs. Thus, this feature cannot be considered universal.

**Hint:** Check if the reproductive method applies to every species within the group.

### Step 4: Analyze Option D - Warm-Blooded Nature
- Most mammals are warm-blooded (endothermic), meaning they can regulate their body temperature. However, there are exceptions, such as certain species like the Arctic ground squirrel or mole rat that exhibit cold-blooded characteristics. Therefore, this feature is not universal.

**Hint:** Consider the ability to maintain body temperature and if there are exceptions in the group.

### Conclusion:
After analyzing all the options, the only feature that is present in all mammals without exception is the diaphragm. Therefore, the correct answer is:

**Answer:** Option B - Diaphragm.