Directions: Read the passage given below and answer the question that follows it.

Early European explorers of the Tropics discovered what they misnamed a louse line. As they went closer to the equator, at some point fleas would abandon the explorers. One explanation is that the heat became too much for the fleas, which may be killed by temperatures even a few degrees higher than 98.6 Fahrenheit, the temperature of a healthy human body. The problem with this explanation is that fleas had been observed abandoning even healthy people when the air temperature in the Tropics was below 98.6 degrees.

Which of the following, if true, most strongly supports the original explanation which the author doubts?

Some species of fleas which occasionally feed on humans can survive at temperatures over 100 degrees.

The so-called louse line was not a latitudinal line like the Tropic of Cancer, but a geographically variable point at which a specific biocritical phenomenon was observed.

For those not acclimated to tropical weather, rises in air temperature cause significant increases in body temperature starting when the air temperature is as low as 85 degrees.

Changes that occurred as the explorers entered the tropics triggered mechanisms in the fleas that were designed to protect the fleas from sick human hosts.

Fleas generally attempt to minimize exposure to the outside elements by hiding under clothes, in hair, and in folds of skin.