Living things have the following characteristics: 1, living things need nutrition; 2. Living things can breathe; 3. Organisms can excrete wastes produced in the body; 4. Biology can respond to external stimuli; 5. Organisms can grow and reproduce; 6. Except for viruses, all living things are composed of cells; Squirrels are constantly looking for food and eating nutrients absorbed by living things from the outside; Stalactites from small to large are natural phenomena, not life phenomena; Puppy urine is a kind of biological waste that can be excreted; Motion sickness and vomiting are creatures that can respond to external stimuli.

So choose: a.