答案：A

解析：

Choice A is correct. In order to produce unbiased, valid data, the sample should be randomly selected and be representative of the entire population of interest. In this case, an appropriately conducted survey should give each consumer aged 18 to 29 years in the city an equal chance of being surveyed.

The choices that involve a particular high school, the chess team, and computer campers would not be representative of the entire population of 18- to 29-year-olds in the city.