Jevais à Lagos _____ les vacances.

The sentence in French is: "Jevais à Lagos _____ les vacances." The aim is to choose the correct preposition to complete the sentence. Here's what each option means:

• pendant: This means "during" in English. In French, it's used to indicate the duration of an action or event. It is appropriate when referring to time periods such as holidays or vacations.
• par: This means "by" or "through" and is typically used to express means or agency, for example, traveling by train ("par train"). It doesn't fit in this context.
• contre: This means "against" and is used when expressing opposition or contact with something. It is not relevant to the context of going somewhere for holidays.
• depuis: This translates to "since" or "for," and indicates the start point of an action that continues. It is not appropriate to use with the concept of spending a vacation somewhere.

Thus, the correct preposition to use in this context is "pendant" because it correctly describes engaging in a trip over a certain duration, particularly during the vacation period. The correct sentence is: "Jevais à Lagos pendant les vacances."