Which of the following is a true statement ?

Options

A. In all mammals, offspring develop within the female
B. All mammals have hair and mammary glands
C. All mammals are land-dwelling forms
D. All of the above

Explanation

To determine which of the statements about mammals is true, let's analyze each option step by step.

### Step 1: Analyze the first statement
**Statement:** "In all mammals, offspring develop within the female."
- **Explanation:** This statement refers to the characteristic of viviparity, where the young develop inside the mother's body and receive nourishment through the placenta. This is true for most mammals, particularly placental mammals.

### Step 2: Analyze the second statement
**Statement:** "All mammals have hair and mammary glands."
- **Explanation:** This statement is also true. All mammals possess mammary glands that produce milk for their young, and they have hair (or fur) at some stage of their life cycle, which is a defining characteristic of mammals.

### Step 3: Analyze the third statement
**Statement:** "All mammals are land-dwelling forms."
- **Explanation:** While the majority of mammals are indeed terrestrial, this statement is misleading. There are mammals that are not land-dwelling, such as aquatic mammals like whales and dolphins. Therefore, this statement is not entirely accurate.

### Step 4: Analyze the fourth statement
**Statement:** "All of the above."
- **Explanation:** Since the first two statements are true but the third is not entirely accurate, the option "all of the above" cannot be considered correct.

### Conclusion
The true statements are the first and second ones. However, the third statement is not universally true for all mammals. Therefore, the answer is that the first two statements are correct, but the option "all of the above" is not true.

### Final Answer
The true statements are:
1. In all mammals, offspring develop within the female.
2. All mammals have hair and mammary glands.

**Correct option:** The first and second statements are true, but "all of the above" is not correct.

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