Please choose the correct ending to complete the given sentence: Pets and Animals: [header] How to ensure passive immunity in newborn puppies [title] Watch the newborn puppies closely. [step] In general, newborn puppies can easily find their mothers' nipples and begin nursing. However, some newborns may have more trouble nursing.

Ending1: If you notice some of the mother's nipples opening up for nursing early in her pregnancy, it's probably because the mother is nursing slowly. [substeps] Observe the newborn puppies closely to ensure they are nursing all the way through their pregnancy. Ending2: Slow baby puppies may find it more difficult to suckle their mother but it is imperative to give them encouragement and excitement instead of waiting around and watching the nursing mother. [substeps] Newborn puppies may cry and resist nursing, so simply provide quiet, positive attention to her by crying or cuddling her. Ending3: First, observe the newborn puppies closely, getting a feel for how they are nursing and where their nipples are located. Then, monitor them for eclampsia within 24 hours of delivery. Ending4: Because colostrum is vital to a newborn puppy's survival, and is available for only a short time after birth, each newborn puppy will need to start nursing almost immediately after birth. [substeps] Watch each newborn puppy to see which ones are nursing and which ones are not.

Answer format: ending1/ending2/ending3/ending4