In mollusks of New York state, which of these experiences gives you a value between 0.1 to 0.2?
( S = log of species richness, A = log of Area, C = log of Y- intercept in the species richness area curve).
(a) `(S-C)/A`
(b) `(S-A)/C`
(c) `(C-A)/S`
(d) `(A-S)/C`

Options

A. `(S-C)/A`
B. `(S-A)/C`
C. `(C-A)/S`
D. `(A-S)/C`

Answer

To solve the question, we need to analyze the relationships given in the context of the species-area relationship described by Alexander von Humboldt. The goal is to determine which of the provided expressions yields a value between 0.1 and 0.2.

### Step-by-Step Solution:

1. **Understanding the Variables**:
- Let \( S \) = log of species richness
- Let \( A \) = log of area
- Let \( C \) = log of y-intercept in the species richness-area curve

2. **Species-Area Relationship**:
- The species-area relationship can be expressed as:
\[ S = C + z \cdot A \]
- Rearranging this gives:
\[ z = \frac{S - C}{A} \]
- This indicates that \( z \) is the slope of the line in a log-log plot of species richness against area.

3. **Analyzing the Options**:
- We need to evaluate the expressions given in the options:
- (a) \( \frac{S - C}{A} \)
- (b) \( \frac{S - A}{C} \)
- (c) \( \frac{C - A}{S} \)
- (d) \( \frac{A - S}{C} \)

4. **Identifying the Correct Expression**:
- From our rearrangement of the species-area relationship, we see that:
\[ z = \frac{S - C}{A} \]
- This matches option (a).

5. **Conclusion**:
- Since \( z \) is known to be between 0.1 and 0.2, the expression that gives a value between 0.1 to 0.2 is:
\[ \text{(a) } \frac{S - C}{A} \]

### Final Answer:
The correct answer is (a) \( \frac{S - C}{A} \).