How about this:
彼女 たち は 日本 語 を 勉強 した こと が あり ます。
Kanojo-tachi wa Nihon-go o benkyō shita koto ga arimasu. Them girls studied japanese at least once.
"Koto" turns every thing preceeding it into a sustantive (noun) clause.
彼女たちは 日本語を 勉強したことが あります。
Kanojo-tachi wa nihon-go o benkyō shita koto ga arimasu.
Them girls studied Japanese at least once.
"ga arimasu" indicates that the subject exists in at least one instance.
- "koto" turns every thing preceding it into a substantive (noun) clause.
- "ga arimasu" indicates that the subject exists in at least one instance.
