Opportunity cost is the value of the next best alternative that must be foregone to undertake an activity. It represents the real cost of a decision.

Here are the answers to all the questions from the image:

1. Opportunity cost is the value of the next best alternative that must be foregone to undertake an activity. It represents the real cost of a decision. The correct option is (d). Answer for 1: $\boxed{\text{real}}$

2. The order of ranking needs according to their importance is a scale of preference. The correct option is (c). Answer for 2: $\boxed{\text{scale of preference}}$

3. Step 1: Arrange the scores in ascending order.

   $$2, 5, 15, 18, 30$$

   Step 2: Identify the