Read the following statement and choose the correct characteristic features of Aves

Options

A. Skin of birds have glands
B. Air sacs help in excretion
C. Heart is having three auricle and one ventricle
D. Preen gland is present at the base of tail

Answer

### Step-by-Step Solution:

1. **Understanding Class Aves**:
- Class Aves consists of all birds. Birds are characterized by certain unique features that distinguish them from other classes of animals.

2. **Identifying Key Features of Aves**:
- **Wings**: The forelimbs of birds are modified into wings, which are essential for flight.
- **Bone Structure**: Birds have hollow bones, known as pneumatic bones, which reduce weight without sacrificing strength.
- **Heart Structure**: Birds possess a four-chambered heart, consisting of two auricles and two ventricles, allowing for efficient circulation.
- **Body Temperature**: Birds are warm-blooded (endothermic), meaning they can regulate their body temperature internally.
- **Skin Characteristics**: The skin of birds is dry and lacks glands, except for a specific gland at the base of the tail.

3. **Analyzing the Options**:
- **Option 1**: "Skin of birds have glands" - Incorrect, as birds' skin is generally dry and lacks glands.
- **Option 2**: "Air sacs help in excretion" - Incorrect, air sacs are involved in respiration, not excretion.
- **Option 3**: "Heart is having three auricles and one ventricle" - Incorrect, birds have a four-chambered heart with two auricles and two ventricles.
- **Option 4**: "Preen gland is present at the base of the tail" - Correct, this gland helps birds maintain their feathers by providing oil for preening.

4. **Conclusion**:
- The correct characteristic feature of Aves from the given options is that the "preen gland is present at the base of the tail."

### Final Answer:
- **The correct characteristic feature of Aves is: Preen gland is present at the base of the tail.**