The correct option is A It conveys the young man's surprise at the little girl's appearance.
The young man seems to know that Sylvia has seen the white heron and he is eager to collect information about the heron from her. So, after she makes her entry, the young man' eagerness has built up an atmosphere of anticipation and suspense for the reader and for the young man himself which increases in intensity as the paragraph continues. This eliminate options B, C and E as not an effect of the tense switch. Option D is, quite evidently, an effect of the tense switch, so D is also out. Only option A does not seem to be an effect of the tense change- the young man's surprise at the little girl's appearance is not evident and her disheveled appearance is stated very matter-of-factly. So, option A is the answer.