hard · GMAT Verbal

Which of the following, if true, most strengthens this conclusion?

1. Most hospital-acquired infections at this facility are transmitted by hand-to-surface contact rather than through the air.
2. At a neighboring hospital, infection rates fell sharply soon after that hospital adopted stricter overnight visitor screening.
3. The hand-sanitizer chosen is independently laboratory-certified to eliminate every one of the known microorganisms it is tested against.
4. Staff members consistently report that the newly installed sanitizer feels noticeably gentler on their skin than ordinary soap and water.
5. The hospital recently expanded its overnight janitorial staff so that shared common areas are now cleaned far more frequently than before.

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