A teacher is experimenting with computer-based instruction. In which situation could the teacher use a hypothesis test for a difference in two population means? (i) She gives each student a pretest. Then she teaches a lesson using a computer program. Afterwards, she gives each student a posttest. The teacher wants to see if the difference in scores will show an improvement. (ii) She randomly divides the class into two groups. One group receives computer-based instruction. The other group receives traditional instruction without computers. After instruction, each student has to solve a single problem. The teachers wants to compare the proportion of each group who can solve the problem. (iii) She gives each student a pretest. She then randomly divides the class into two groups. One group receives computer-based instruction. The other group receives traditional instruction without computers. After instruction, each student takes a post-test. The teacher compares the improvement in scores (post-test minus pretest) in the two groups. (iv) The teacher uses a combination of traditional methods and computer-based instruction. She asks students which they liked better. She wants to determine if the majority prefer the computer-based instruction.