Acronym Soup: PTO ?

Questions

Because of the giant panda's large size and the small size of their offspring, it is difficult to tell when a panda is ----------?

The albatross drinks sea water. It has a special desalinization apparatus that strains out and excretes all excess ----------?

Marine iguanas, saltwater crocodiles, sea snakes, and sea turtles are the only surviving seawater-adapted ----------?

Frogs never drink. They absorb water from their surroundings by ----------?

Because of their acute sense of smell, dogs are trained to sniff out everything from drugs to bombs to iron ore. In Ontario, Canada, instruments couldn't locate where natural gas was escaping from a pipeline buried 18 feet underground. Trained ---------- were brought in. The dogs worked in sub-zero temperatures and covered nearly 100 miles of frozen ground, ultimately finding more than 150 gas leaks.?