Questions & Answers about Ŝi aĉetis eksterlandan biciklon.
Because it is the direct object of the verb aĉetis (bought).
In Esperanto, the direct object usually takes the ending -n. So:
- biciklo = a bicycle
- biciklon = a bicycle, as the thing being bought
In this sentence, she is doing the action, and the bicycle is receiving the action, so biciklon gets -n.
Because adjectives must agree with the nouns they describe.
Since biciklon is:
- singular
- adjective-compatible
- in the accusative case (-n)
the adjective must match it:
- eksterlanda biciklo = a foreign bicycle
- eksterlandan biciklon = a foreign bicycle, as the direct object
This agreement is a very important feature of Esperanto.