Plutonium is much rarer in nature than uranium and is more commonly used for bombs rather than as reactor fuel. Like uranium, it comes in various isotope forms, with plutonium 239 the most commonly used. It is mixed with the much more unstable plutonium 240 to generate power.
It's my understanding that a horse's knees close around age 2- 2 1/2. My gelding JUST turned 3. A couple days ago in fact. Will a horse's knees almost certainly be closed by that age?
This movement strengthens leg muscles, and your infant will need that strength to roll over, which will probably happen around 4 to 6 months of age. (But be careful: Even very young babies can roll over on occasion, so it's important to never leave a baby unattended on a changing table, bed, or other high surface.)