Seema crossed pure breed pea plants having round-yellow seeds with wrinkled green seeds and found that only A-B type of seeds were produced in the `F_1` generation. When `F_1` generation pea plants having A-B type of seeds were cross-breed oy self pollination, then in addition to the original found yellow and wrinkled green seeds, two new varieties A-D and C-B types of seeds were also obtained.
The above cross is known as

Options

A. Monohybrid cross
B. Dihybrid cross
C. Test cross
D. Back cross

Explanation

To determine the type of cross that Seema performed with the pea plants, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Traits Involved**:
- Seema crossed purebred pea plants with two traits: seed shape (round vs. wrinkled) and seed color (yellow vs. green).
- Round seeds (R) and yellow seeds (Y) are dominant traits, while wrinkled seeds (r) and green seeds (y) are recessive traits.

2. **Analyze the F1 Generation**:
- The F1 generation produced only one type of seed, which is the dominant phenotype (round-yellow seeds, represented as AB).
- This indicates that all offspring from the cross of round-yellow seeds with wrinkled-green seeds exhibit the dominant traits.

3. **Self-Pollination of F1 Generation**:
- When the F1 generation (AB) was self-pollinated, the resulting offspring showed a variety of combinations: round-yellow (AB), wrinkled-green (ab), and two new combinations (AD and CB).
- The appearance of these new combinations suggests that two traits were segregating independently.

4. **Determine the Type of Cross**:
- Since two traits (seed shape and seed color) were involved in the initial cross and both traits segregated in the F2 generation, this indicates that the cross is a **dihybrid cross**.
- A dihybrid cross involves two different traits, which is consistent with the traits studied by Seema.

5. **Conclusion**:
- Therefore, the cross performed by Seema is known as a **dihybrid cross**.

### Final Answer:
The above cross is known as **B. Dihybrid cross**.