Question

scientists can usually predict when a tsunami will occur, but they cannot
a determine if an earthquake has occurred.
b measure earthquakes that occur in the ocean.
c predict how large the waves will be.
d estimate when the waves will reach land.

Explanation:

Scientists can detect earthquakes (ruling out A), measure ocean - based earthquakes (ruling out B), and estimate wave arrival times (ruling out D). However, predicting the exact size of tsunami waves is difficult.

Answer:

C. predict how large the waves will be.