Answer:
A. When you are talking about yourself
Step-by-step explanation:
When conjugating verbs, the form that ends in -o is typically used when speaking about yourself, or in the point of view of 'I' or 'me'.
For example:
Me ducho por la mañana. ( I shower in the morning. )
or
Yo como comida. ( I eat food. )
Therefore, the verb Duchar (to shower) or Comer (to eat) ends in -o because you are talking about yourself.