DNA can be introduced into any cell by:

Options

A. Injection
B. Being complexed with calcium salts
C. Being placed along with the cell into a gene gun
D. Gel electrophoresis

Answer

To solve the question "DNA can be introduced into any cell by:", we need to analyze the given options and determine which method allows for the introduction of DNA into a wide variety of cells.

### Step-by-Step Solution:

1. **Understanding the Options**: We have four options to consider:
- A) Injection
- B) Being complexed with calcium salt
- C) Being placed along with a cell into a gene gun
- D) Gel electrophoresis

2. **Analyzing Option A - Injection**:
- Injection can transfer DNA into specific cells, such as during IVF procedures, but it is not a universal method for all cell types. Therefore, this option is not suitable for introducing DNA into any cell.

3. **Analyzing Option B - Being complexed with calcium salt**:
- Calcium salts can facilitate the uptake of DNA by breaking down cell walls, allowing DNA to enter various types of cells. This method is known as calcium phosphate transfection and is effective for a broad range of cells. This option appears promising.

4. **Analyzing Option C - Being placed along with a cell into a gene gun**:
- A gene gun uses a particle delivery system to introduce DNA into cells, typically using metal particles coated with plasmid DNA. While effective, it is not universally applicable to all cell types, as not all cells can take up the metal-coated particles.

5. **Analyzing Option D - Gel electrophoresis**:
- Gel electrophoresis is a technique used for separating macromolecules based on size and does not involve the introduction of DNA into cells. Thus, this option is irrelevant to the question.

6. **Conclusion**:
- After analyzing all options, the most effective and universal method for introducing DNA into any cell is **being complexed with calcium salt**. Therefore, the correct answer is option B.

### Final Answer:
**B) Being complexed with calcium salt**