Answer: b. people face trade-offs
Explanation:
From the question, we are informed that Bullie Jean has $120 to spend and wants to buy cither a new amplifier for her guitar or a new mp3 player to listen to music while working out.
We are further informed that the amplifier and the mp3 player cost $120, each and so she can only buy one. This shows that people face trade offs and have to make a choice regarding some decisions. Here, an opportunity cost will be the one that she didn't buy at the expense of the other.
A space probe is an unmanned instrumented spacecraft that is designed to execute physical studies of space environment. It is rocketed into space with enough speed to achieve the velocity needed to obtain hyperbolic orbit and also to reach a trajectory that is aimed at a pre-selected target.
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A tariff is a tax on exported goods, if a tariff is too high then it will increase the cost of the item so the people who are buying have to pay more.