Answer:
C. not valid; There is bias because of the location where people are asked.
Explanation:
A reporter wants to know the percent of people who want more parks to be built. He surveys 50 people at random at a local park.
This sampling is biased as the reporter is asking the people who are already in the park.
The people who are already in the park, can definitely say yes to more parks.
Rather, the reporter should have surveyed people outside the park.
So, the answer is - Not valid; There is bias because of the location where people are asked.