medium · SAT Reading & Writing

Roman harbor concrete has stood in seawater for two thousand years, and researchers credit the volcanic ash in the mix, which reacts with saltwater to grow interlocking crystals that seal cracks as they form. ______ modern marine concrete depends on steel reinforcement and typically begins to spall within a few decades of exposure. Which choice completes the text with the most logical transition?

1. By comparison,
2. Additionally,
3. Indeed,
4. Therefore,

Sign up free to see the explanation and track your rank →