We had ought to finish our trip before dark because it gets very cold after the sun goes down.

Explanation: The phrase 'had ought to' is grammatically incorrect as 'ought' already expresses obligation, and 'had' is redundant. The correct form is simply 'ought to.' Incorrect options: B. 'Because' is correctly used to introduce a reason. C. 'It' correctly refers to the situation. D. 'Goes down' is appropriately used for the sun setting. Note: 'Had ought to' is considered archaic or incorrect in modern English usage.