(4) Each day they got worse; soon it became clear that mere adjectives could not convey any idea of their terrors. Therefore I devised a mosquito gauge. I held up a bare hand for 5 seconds by the watch, then counted the number of borers on the back; there were 5 to 10. Each day added to the number, and when we got out to the Buffalo country, there were 15 to 25 on the one side of the hand and elsewhere in proportion.

How does this paragraph further develop the author's idea about the Northern Territory mosquitoes?

A.
By using his gauge, he shows how swarming the mosquitoes are as they travel north.
B.
The author is directly contrasting his data with Dr. Howard's New Jersey data.
C.
He describes a gauge he developed in order to track the speed of the mosquitoes.
D.
He explains how the mosquitoes terrorized him and his crew during their field studies.