Translation of oxide in Spanish

Lili was very nervous and feared that the entrance would be denied because she did not have any blank pages in the passport. The Visa office took our papers and pictures and handed them back five minutes later.
I understand that you use the article 'die' when talking about a feminine object, das when the subject is neutral, and der when talking about a masculine object. But how can you remember all these?
The next morning we got up at 4.30. At sunrise, one hour later, a taxi waited for us in front of the hotel. He would take us on a 2 hours private sightseeing tour around Arequipa, just before traffic started.