41.
(A) investigate
(B) endanger
(C) detect
(D) stalk

Many animals depend upon sound to find food, detect predators and communicate with one another.
許多動物依靠聲音尋找食物、發現捕食者並相互交流。

(A) investigate
to examine a crime, problem, statement, etc. carefully, especially to discover the truth
（尤指為揭開真相）調查，審查
Police are investigating allegations of corruption involving senior executives.
We are of course investigating how an error like this could have occurred.

(B) endanger
to put someone or something at risk or in danger of being harmed, damaged, or destroyed
使處於險境；危及；危害
He would never do anything to endanger the lives of his children.
We must be careful not to do anything that might endanger the economic recovery.

(C) detect
to discover something, usually using special equipment
（通常指用特別設備）探測，檢測，測出
High levels of lead were detected in the atmosphere.
Radar equipment is used to detect (= find the position of) enemy aircraft.
to notice something that is partly hidden or not clear, or to discover something, especially using a special method
（尤指用特殊方法）發現，察覺，看出
Some sounds cannot be detected by the human ear.
Financial experts have detected signs that the economy is beginning to improve.

(D) stalk
the main stem of a plant, or the narrow stem that joins leaves, flowers, or fruit to the main stem of a plant
（植物的）莖，稈；（葉或果實的）柄，蒂；（花）梗
She trimmed the stalks of the tulips before putting them in a vase.
to follow an animal or person as closely as possible without being seen or heard, usually in order to catch or kill them
跟蹤，悄悄地靠近（獵物或人）
The police had been stalking the woman for a week before they arrested her.
If something unpleasant stalks a place, it appears there in a threatening way.
（令人不快的事）籠罩
When night falls, danger stalks the streets of the city.
to walk in an angry or proud way
怒氣衝衝地走；趾高氣揚地走
She refused to accept that she was wrong and stalked furiously out of the room.

資料來源：劍橋辭典