文7課 指示表現「こ・そ・あ」 教科書 p.144〜147
Directive — distinguishes こ/そ/あ in text
用法：あれ・あの・あのころ
Use あ系 when both writer and reader know (shared memory).
注意 / Note：Therefore, in explanatory writing, あ系 is rarely used; often found in recollection: あのころ・あの事件.
比較 / Compare：あ系 = shared memory of writer and reader → rarely used in expository writing.
よく出る形 / Common form：Flashback: あのころ・あの事件・あの時代.
あのころは、だれもが貧しかった。
At that time, everyone was poor.（common memory）
あの事件以来、町の様子は変わってしまった。
Since that incident, the town's landscape has changed.
あの時代を経験した人は、もう多くない。
There are not many people who went through that time anymore.