Today, at home, Japanese, approximately 3 hours about, even, studied. [Syntax]

The correct answer is "ぐらい". "ぐらい" is used after a quantity, time, or duration to indicate an approximation, meaning "about" or "approximately". It correctly follows "３じかん" (3 hours) to form "３じかんぐらい" (about 3 hours), which specifies the approximate duration of studying. This is a common way to express estimation.

正解は「ぐらい」です。量（りょう）や時間（じかん）などの後に付けて、「おおよそ～くらい」という意味を表します。「３じかんぐらい」で「約（やく）3時間」となります。「だいたい」と合わせて、おおよその時間を示します。