The long-day plant is

Options

A. Wheat/Spinach
B. Soyabean
C. Tobacco
D. Xanthium

Answer

**Step-by-Step Solution:**

1. **Understanding Long-Day Plants**: Long-day plants are those that require a longer duration of sunlight to trigger flowering. This means they typically bloom when the days are longer, which occurs in the summer months.

2. **Contrast with Short-Day Plants**: In contrast, short-day plants require longer periods of darkness to flower. They tend to bloom in the spring or fall when the days are shorter.

3. **Identifying Examples**: To answer the question, we need to identify which of the provided options are classified as long-day plants.

4. **Evaluating the Options**:
- **Option A**: Wheat and spinach - Both are known to be long-day plants.
- **Option B**: Soya bean - This is generally classified as a short-day plant.
- **Option C**: Tobacco - This plant can be classified as a day-neutral plant, but it is not primarily a long-day plant.
- **Option D**: Xanthium - This plant is also typically considered a short-day plant.

5. **Conclusion**: Based on the definitions and examples, the correct answer is **Option A: Wheat and Spinach**.