Re: At / in church Yes. On the beach means literally on the beach:
Much driftwood lay on the beach after the storm. At the beach is more general: At the beach there are several seafood restaurants. (These restaurants are probably not literally on the beach, but more likely on solid ground directly adjacent to the beach.
Thus: 'We spent the whole dayon the beach,' means we spent the whole day lying on the sand, splashing in the water, flying kites, building sand castles, etc., etc. 'We spent the whole day at the beach,' could mean we drove to our beach house (which is very near the beach), we played on the beach, we ate at a beach restaurant (near the beach), we took an evening stroll on the beach, etc. etc.
I hope this is helpful,
Petra |