The following ratio is generally constant for a given species

Options

A. A+G/C+T
B. T+C/G+A
C. G+C/A+T
D. A+C/T+G

Explanation

To solve the question regarding which ratio is generally constant for a given species, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Context**: The question is asking about a ratio that remains constant within a species. This relates to the composition of nucleotides in DNA.

2. **Identify the Options**: We have three options:
- Option 1: Adenine (A), Guanine (G), Cytosine (C), Thymine (T)
- Option 2: Thymine (T) + Cytosine (C) and Guanine (G) + Adenine (A)
- Option 3: Guanine (G) + Cytosine (C)

3. **Recall Chargaff's Rules**: According to Chargaff's rules:
- Adenine (A) pairs with Thymine (T)
- Guanine (G) pairs with Cytosine (C)
- The ratio of (A + T) to (G + C) is constant for a given species.

4. **Analyze Each Option**:
- **Option 1**: This does not represent a specific ratio; it lists the nucleotides.
- **Option 2**: This option compares the sum of T + C with G + A, which is not the ratio that Chargaff specified.
- **Option 3**: This option states G + C, but it does not provide a ratio in relation to A + T.

5. **Determine the Correct Answer**: The correct ratio that remains constant in a given species is the ratio of (A + T) to (G + C). However, since this option is not explicitly listed, we can infer that the question is asking for the relationship that is consistent across species.

6. **Final Conclusion**: Based on Chargaff's rules, the ratio of (A + T) to (G + C) is the one that is constant for a given species.

### Answer:
The ratio that is generally constant for a given species is the ratio of (Adenine + Thymine) to (Guanine + Cytosine).