Answer:
D, all students in each grade.
Explanation:
If you did a random sample from the students in the speech club it will be biased because they will probably all say giving speeches because they are in the speech CLUB. You cannot do the teahcers because their answers will also be biased. If you do all the boys in each grade it will be biased only to what boys like and not girls or any other student in the grade. Therefore, using the process of elimination, the answer is D, you should take a random sample of all the students in each grade.