What is a private good? Give an example of a private good? What is a public good? Give an example of a public good that you use almost everyday?

PLEASE HELPPP I NEED IT

One drawback of voluntary trade is that it a. requires two groups to use a common language b. can make one group dependent upon another for necessary goods c. doesn't occur unless there is a shortage of goods for at least one group d. forces groups to rely on themselves to produce all the goods they need