Complete dominance occur in
(a) Mirabilis jalapa
(b) Oenothera lamarckiana
(c) Pisum sativum
(d) Lathyrus odoratus

Options

A. Mirabilis jalapa
B. Oenothera lamarckiana
C. Pisum sativum
D. Lathyrus odoratus.

Answer

To determine which plant exhibits complete dominance, we need to analyze each option based on the principles of inheritance.

### Step-by-Step Solution:

1. **Understanding Complete Dominance**:
- Complete dominance occurs when the dominant allele completely masks the effect of the recessive allele in a heterozygous individual. This means that only the dominant phenotype is expressed when at least one dominant allele is present.

2. **Analyzing Each Option**:
- **Option (a) Mirabilis jalapa**:
- This plant exhibits incomplete dominance, where the phenotype of the heterozygote is an intermediate between the two homozygous phenotypes. Thus, it does not show complete dominance.

- **Option (b) Oenothera lamarckiana**:
- This plant does not exhibit complete dominance either. It shows a different inheritance pattern that does not conform to the typical 3:1 ratio associated with complete dominance.

- **Option (c) Pisum sativum**:
- The pea plant, studied extensively by Gregor Mendel, is a classic example of complete dominance. Mendel observed that when he crossed different varieties of pea plants, the dominant traits completely masked the recessive traits in the offspring, resulting in a 3:1 phenotypic ratio in the F2 generation.

- **Option (d) Lathyrus odoratus**:
- Similar to Mirabilis jalapa, Lathyrus odoratus also exhibits incomplete dominance, where the heterozygous phenotype is a blend of the two homozygous phenotypes.

3. **Conclusion**:
- Based on the analysis, the correct answer is **(c) Pisum sativum** as it is the only plant among the options that exhibits complete dominance.

### Final Answer:
(c) Pisum sativum