Ken enjoys bird watching. every summer, he sees many ruby-throated hummingbirds in his garden. however, during the winter, he never sees any ruby-throated hummingbirds. which of the following is a testable hypothesis that ken could make to explain the winter absence of the hummingbirds?

the correct answer is 2 and 4

photosynthesis makes the glucose that is used in cellular respiration to make atp. the glucose is then turned back into carbon dioxide, which is used in photosynthesis. while water is broken down to form oxygen during photosynthesis, in cellular respiration oxygen is combined with hydrogen to form water.