Obligate parasities are those organisms which :

Options

A. live only on living host
B. live only on dead and decaying organic matter
C. are essentially saprophytes but also can become parasites
D. are essentially parasites but also can become saprophytes.

Answer

**Step-by-Step Solution:**

1. **Understanding Parasites**:
- Parasites are organisms that depend on a host for their food and survival. They typically benefit from this relationship while harming the host.

2. **Defining Obligate Parasites**:
- The term "obligate" means strict or necessary. Therefore, obligate parasites are those that have a strict requirement for a living host to survive.

3. **Characteristics of Obligate Parasites**:
- Obligate parasites cannot live or reproduce without their host. If the host is not present, these parasites will not survive.

4. **Differentiating from Other Types of Parasites**:
- Unlike facultative parasites, which can survive in both living hosts and in decaying organic matter, obligate parasites are strictly dependent on living hosts.

5. **Conclusion**:
- Based on the definition and characteristics, obligate parasites are organisms that live only in living hosts.

**Final Answer**: Obligate parasites are those organisms which live only in the living host.

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