The correct answer is d) before eating breakfast.
The paragraph explains that birds sing at daybreak because it's too dark to find food, and singing in the dark would attract predators. So, they wait until dawn to sing, and then they go looking for food once it's bright enough. Therefore, the correct answer is d) before eating breakfast, as the singing occurs before they begin their search for food.
Options a) to warn of predators, b) in the dark, and c) in chorus are not correct based on the information provided in the paragraph. While it's mentioned that singing in the dark would attract predators, the main purpose of the singing is not to warn of predators. Additionally, the paragraph states that birds sing at daybreak, not in the dark, and while the paragraph mentions that birds sing in a chorus, this is not the main focus of the paragraph.