Final answer:
The sight of a single plane caused more terror and disruption of normal life than the appearance of many hundreds of planes before the atomic bombings.
Step-by-step explanation:
The highlighted phrase that explains what sight caused the terror Japanese people experienced after the atomic bombings of Hiroshima and Nagasaki is:
persons who had become accustomed to mass air raids had grown to pay little heed to single planes or small groups of planes, but after the atomic bombings the appearance of a single plane caused more terror and disruption of normal life than the appearance of many hundreds of planes had ever been able to cause before.
This passage highlights the psychological impact of the atomic bombings, where the sight of a single plane instilled more fear and panic than previous air raids. The utter destruction caused by the atomic bombs created a level of terror that surpassed anything experienced before.