4. Why is someone who surreptitiously(秘密地) listens to others' conversations called an eavesdropper?
Eavesdropping isn't exactly an endearing(讨人喜欢的) activity today, but from the sixteenth through the nineteenth centuries, eavesdropping was a crime in England. Back then, communities were not equipped with gutter systems(屋顶的檐槽系统), so houses were surrounded by eavesdrops, spaces all around a building where water dripped from the eaves(屋檐). The purpose of the eavesdrop was to allow a wide overhang so that rain fell far enough from the house to safeguard the security of the foundation.
The first eavesdroppers were nefarious(极坏的) types who literally stood in the eavesdrops to overhear private conversations. Protected from the elements by the overhang, this low-tech espionage(间谍活动) evidently faded as sewer systems(下水道系统) rendered(致使) eavesdrops obsolete(过时的，废弃的).