Misc: What element does the chemical symbol ca stand for?

Questions

"The hardest thing in life is to know which ---------- to cross and which to burn."- David Russell?

"If we knew what it was we were doing, it would not be called ------------, would it?"- Albert Einstein (1879-1955)?

"The hardest thing to understand in the world is the ."- Albert Einstein (1875-1955)?

"If we want things to stay as they are, things will have to ---------."- Guiseppe di Lampedusa (1896 - 1957)?

"If ------------ didn't exist, all the money in the world would have no meaning."- Aristotle Onassis (1906-1975)?