Fact 1: Plants release oxygen during the day but not during the night. Fact 2: Plants include blue pine, hemlock, spruce and oak. Given the two facts above, what releases oxygen during the day but not during the night?

Choose your answer from: a). elephants b). dogs c). hydrocarbons d). blue pine e). Conifers f). vegetation g). humans h). Fuel cells
The answer is:
d).