21 Which of the following is an appropriate title for this passage?
(A)The Pros and Cons of Alarm Pheromones
(B)How the Nose Sniffs Danger in the Air
(C)The Evolution of the Grueneberg Ganglion
(D)The Contribution of Hans Grueneberg

The next time someone says, “I smell danger in the air,” that might literally確實地；名副其實地, 逐字 be true. At the tip of the noses of mammals哺乳動物 is a ball of nerve神經 cells known as the Grueneberg格吕内贝格 ganglion神經節, named after Hans Grueneberg, the scientist who described the structure結構；構造 in mice in 1973.

Grueneberg thought it was just a nerve ending. Only in the last few years did scientists realize that the Grueneberg ganglion神經節 is a component組成部分；成分；零件 of the olfactory嗅覺 system.

But they still did not know what the ganglion神經節 smelled. Recently, researchers in Switzerland report that they have figured it out.

All sorts種類，類型 of organisms生物體；有機體；微生物, including plants, insects, and mammals, release “alarm pheromones” when they sense能力, 官能；感覺 danger; the pheromones waft（在空氣中）飄盪 through the air to warn others.

Very little is known about the alarm pheromones of mammals other than that they exist.

Nonetheless然而，但是；儘管, the Swiss scientists could collect the pheromones by simply stressing焦慮, 緊張，壓力 mice and sucking up吸收 the air around them.

When other normal mice were exposed暴露；露出 to the danger-scented香的，芬芳 air, they froze in their tracks道路, （鐵路的）軌道.

But mice whose Grueneberg ganglia had been removed did not notice anything wrong and continued to wander around their cages籠子 without a care in the world.

補充：literal翻譯：（意義）字面的，根本的, 逐字（翻譯）的。

Which of the following is an appropriate title for this passage? 
(A)The Pros and Cons贊成者和反對者 of Alarm Pheromones 

(B)How the Nose Sniffs嗅，聞 Danger in the Air 

(C)The Evolution of the Grueneberg Ganglion 
(D)The Contribution貢獻，奉獻 of Hans Grueneberg