In which of the following pair of animals does oestrous cycle takes place?

Options

A. Cow and rat
B. Human and rat
C. Gorilla and tiger
D. Monkey and gorilla

Answer

To determine which pair of animals undergoes the estrous cycle, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Estrous Cycle**: The estrous cycle is a reproductive cycle found in many mammals, where the endometrium (the lining of the uterus) is not shed if fertilization does not occur. Instead, it is reabsorbed. This cycle is typical in non-primate mammals.

2. **Identify the Types of Reproductive Cycles**: There are two main types of reproductive cycles in mammals:
- **Estrous Cycle**: Common in non-primate mammals (e.g., cows, rats).
- **Menstrual Cycle**: Common in primates (e.g., humans, gorillas, monkeys), where the endometrium is shed if fertilization does not occur.

3. **Analyze the Given Options**:
- **Cow and Rat**: Both are non-primate mammals and typically exhibit the estrous cycle.
- **Human and Rat**: Humans are primates (menstrual cycle), and rats are non-primates (estrous cycle).
- **Gorilla and Tiger**: Gorillas are primates (menstrual cycle), and tigers are non-primates (estrous cycle).
- **Monkey and Gorilla**: Both are primates and exhibit the menstrual cycle.

4. **Determine the Correct Pair**: Since the estrous cycle is found in non-primates, the only pair that fits this criterion is **Cow and Rat**.

5. **Conclusion**: Therefore, the correct answer to the question is **Cow and Rat**.

### Final Answer:
The pair of animals in which the estrous cycle takes place is **Cow and Rat**.

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