Passage Summary: After a stroke, some patients' brain cells keep dying, and these patients have high levels of a specific protein. Since that protein is known to kill cells when it leaks, it's likely the cause of the ongoing damage.

Conclusion: The leakage of glutamate from damaged nerve cells is a cause of long-term brain damage following a stroke.

Reasoning: Patients with the most cell death also had the highest glutamate levels, and glutamate is known to be toxic to surrounding cells when it leaks out of damaged ones.

Analysis: The argument moves from a correlation (high glutamate and cell death) and a known mechanism (glutamate kills cells) to a causal conclusion. To strengthen this, look for an answer that reinforces the causal link or rules out an alternative. For instance, showing that the damage stops if the glutamate is blocked would provide powerful support for the author's claim.