a perfectly round pearl的用法和样例：
- She has a perfectly round pearl.
- The dough must be kneaded, shaped and coaxed into a perfectly round disc by hand.
- They started out very simply, with a perfectly round area in a crop where the grain was flattened in certain ways.
- And at Versailles, we plant these conically cut trees in pairs and arrange them with perfect symmetry along a perfectly round circle or in perfectly rectilinear rows in army formation.