To determine which measurement generally predicts pregnancy failure, we need to compare the given values and choose the largest one. Here are the steps to solve this problem:
1. Convert to a common unit: All measurements should be in the same unit for accurate comparison. We'll convert all values to millimeters (mm).
2. Given values in millimeters:
- \( a = 10 \, \text{mm} \)
- \( b = 1.5 \, \text{cm} \rightarrow 1.5 \times 10 = 15 \, \text{mm} \) (since 1 cm = 10 mm)
- \( c = 2.0 \, \text{cm} \rightarrow 2.0 \times 10 = 20 \, \text{mm} \) (since 1 cm = 10 mm)
- \( d = 25 \, \text{mm} \)
3. Compare the values:
- \( 10 \, \text{mm} \)
- \( 15 \, \text{mm} \)
- \( 20 \, \text{mm} \)
- \( 25 \, \text{mm} \)
4. Identify the largest value: Among the measurements, the largest value is \( 25 \, \text{mm} \).
Therefore, a gestational sac with a mean sac diameter greater than 25 mm generally predicts pregnancy failure.
