The preposition "over" is used when referring to a duration that spans multiple days or a period of time, such as a weekend. In this sentence, "over the weekend" means that the reading will take place at some point during the weekend, covering a part or the whole of that time. So, the correct preposition to use in this sentence is "over" because it indicates an action that will take place throughout the duration of the weekend.
• "In the weekend" (option a): Incorrect. "In" is typically used for longer time periods like "in July" or "in the 21st century," but not for a short time span like a weekend.
• "On the weekend" (option b): Incorrect. "On" is used for specific days, e.g., "on Saturday," but not when referring to a general duration like the whole weekend.
• "At the weekend" (option d): Incorrect because "at" is generally used for specific points in time, not for a duration like a weekend.
• "Through the weekend" (option e) would imply the action continues from the beginning to the end of the weekend without stopping, which doesn't fit the meaning of casually reading a book.
Thus, the correct answer is option (c) "over".