Economic Questions! True, False, or Uncertain!?

I have four questions that I have to answer either true, false, or uncertain and they are: 1) Monoplies always charge the highest possible price. 2) To find a monopoly, look for bigness. For example, a monopoly is more likely to be found in the oil business than in the dry-cleaning business. 3) If all the... show more I have four questions that I have to answer either true, false, or uncertain and they are:
1) Monoplies always charge the highest possible price.
2) To find a monopoly, look for bigness. For example, a monopoly is more likely to be found in the oil business than in the dry-cleaning business.
3) If all the companies in an industry raise their prices at the same time, one can be pretty sure that there is collusion or monopoly behavior in this industry.
4) If marginal cost equals marginal revenue, a firm must be breaking even, because costs and revenues are equal.

This is what I answered for each:
1) False
2) False
3) Uncertain
4) False

I would like to make sure these are correct and could you please provide an explanation so I can understand why you answered the question the way you did?
Thank-you
4 answers 4