Answer:
B. Bias.
C. Error.
Step-by-step explanation:
Two of the biggest problems that can occur when generating or collecting valid data are Bias and Errors. Biases automatically make the collected data invalid since this causes the data those involved to purposefully skew the data towards the direction that best suits their biases/beliefs which makes the entire study invalid and therefore the data as well. The second main problem would be human error such as entering the wrong data numbers, choosing the wrong subject, losing the data itself, etc. Humans make mistakes and making one during a study can immediately invalidate all of the data that has been collected.