Questions & Answers about Puer clavem tenet et ianuam aperit.
Both clavem (key) and ianuam (door) are direct objects, so they are in the accusative singular. You can tell partly by form:
- clavis (nom. sg., 3rd declension) → clavem (acc. sg.)
- ianua (nom. sg., 1st declension) → ianuam (acc. sg.) And you can tell by function: they are the things being held and opened.