Answer:
1. a portion of a large group - sample
A sample is a small part out of a large population.
2. choosing a sample so that every member has an equal chance of being chosen - random sample
Random sampling gives equal chance to each sample to be considered for the survey.
3. choosing a sample from people who are under 15 years old - biased sample
A biased sample is that which is based on some criteria and nor random.
4. using the responses of a small group to make conclusions about the large group - estimating from a sample