Horizontal asymptote is what happens to T(f) as t becomes extremely large (approaches infinity). The horizontal asymptote is the line which T(t) approaches as t goes to infinity, i.e. the line y=0. This means that the person's body temperature will approach 0ºF above 98.6ºF as t goes to infinity. i.e. the person's body temperature will approach 98.6ºF as time lapses.
The first option.
-Hops