Final answer:
The truth of the statement regarding the annual euthanization of 1.5 million shelter animals cannot be confirmed without specific, up-to-date statistical data. The reference provided does not cover this topic, and thus, we cannot accurately answer true or false.
Step-by-step explanation:
The statement in question appears to be related to the euthanization statistics of shelter animals and does not connect directly to the provided reference information related to scientific use of animals, or the options listed which encompass various biology topics such as climate change, invasive species, zoonotic diseases, and overharvesting. As such, without up-to-date and specific data regarding the exact number of shelter animals euthanized yearly, we cannot reliably confirm the truth of the statement that 'Each year, 1.5 million shelter animals are euthanized.' Therefore, if we are to make sure we provide an accurate answer based on the provided reference, we should avoid affirming the statement as true or false without the appropriate statistical evidence.