Un, an easy way to tell is through the ending vowel.
The 'o' in boligrafo is masculine, so the there are two automatic answers brought forward, 'un', and 'el'.
Then, in english, it would be like saying 'the' or 'a' whereas the is either 'el' or 'la', while a a 'un' or 'una' respectively.
Clock: reloj. half past: medio de. to/before: antes de. quarter past: y cuarto.
Answer:
nose no entiendo es un poema ?
Explanation: