The reason that the chemical/synthetic fertilisers should be replaced by biofertilisers is that the former

Options

A. are source of environmental pollution
B. are expensive
C. exhaust the valuable energy resources for their manufacture
D. all of these

Explanation

**Step-by-Step Solution:**

1. **Understanding Biofertilizers:**
- Biofertilizers are substances that contain living microorganisms which help in enhancing the nutrient quality of the soil. They improve soil fertility by increasing the availability of essential nutrients to plants.

2. **Identifying Issues with Chemical/Synthetic Fertilizers:**
- Chemical or synthetic fertilizers are known to have several drawbacks:
- **Environmental Pollution:** These fertilizers can lead to soil and water pollution. When they are used excessively, they can leach into water bodies, causing eutrophication and harming aquatic life.
- **Cost:** Chemical fertilizers can be expensive to produce and purchase, which can be a burden for farmers.
- **Energy Resource Exhaustion:** The manufacturing process of chemical fertilizers consumes significant amounts of energy, depleting valuable energy resources.

3. **Evaluating the Options:**
- Option 1: Source of environmental pollution - **True**
- Option 2: Are expensive - **True**
- Option 3: Exhaust the valuable energy resources for their manufacture - **True**
- Option 4: All of these - Since all the previous options are true, this option is also correct.

4. **Conclusion:**
- Given the negative impacts of chemical fertilizers on the environment, their high costs, and the energy resources they consume, it is reasonable to replace them with biofertilizers. Therefore, the correct answer is **Option 4: All of these.**