Study the following statements.
1. Chromosomes are located in the nucleolus. 2. Genes are located in the chromosomes. 3. Unicellular organisms respire and reproduce. 4. The most important function of cell membrane is to control the entry and exist of material from cells.
The correct statements are

Options

A. 1, 3 and 4
B. 1, 2 and 4
C. 1, 2 and 3
D. 2, 3 and 4

Explanation

To determine which statements are correct, let's analyze each statement one by one.

### Step 1: Analyze the First Statement
**Statement 1:** Chromosomes are located in the nucleolus.
- This statement is **incorrect**. Chromosomes are located in the **nucleus** of the cell, not in the nucleolus. The nucleolus is a structure within the nucleus where ribosomal RNA is produced.

### Step 2: Analyze the Second Statement
**Statement 2:** Genes are located in the chromosomes.
- This statement is **correct**. Genes, which are segments of DNA, are indeed located on chromosomes. Chromosomes are structures that contain genetic information.

### Step 3: Analyze the Third Statement
**Statement 3:** Unicellular organisms respire and reproduce.
- This statement is **correct**. Unicellular organisms, such as bacteria and protozoa, perform respiration and can reproduce, either asexually or sexually.

### Step 4: Analyze the Fourth Statement
**Statement 4:** The most important function of the cell membrane is to control the entry and exit of material from cells.
- This statement is **correct**. The cell membrane regulates what enters and exits the cell, maintaining homeostasis and allowing communication with the external environment.

### Conclusion
Based on the analysis:
- **Correct Statements:** 2, 3, and 4.
- **Incorrect Statement:** 1.

### Final Answer
The correct statements are: **two, three, and four.**

---