Step 1: Understanding the preposition use.
In Spanish, the preposition “por” is used to indicate time periods during which an action takes place, especially with parts of the day (mañana, tarde, noche, madrugada).
Step 2: Apply the rule.
The expression “por la madrugada” means “in the early morning.” Hence, when talking about departure time, we say:
“Salimos para Berlín por la madrugada.”
Step 3: Analysis of options.
- (1) con → Incorrect; not used for time reference.
- (2) a → Incorrect; used for direction or movement.
- (3) de → Incorrect; does not indicate time.
- (4) por → Correct; used with time expressions (por la mañana, por la noche).
Step 4: Conclusion.
Therefore, the correct sentence is:
“Mañana salimos para Berlín por la madrugada.”