The following practice text comes from http://www.esl-lounge.com/student/grammar/2g31-penguin-story.php:
One day a husband and wife _____ (1) (drive) to the countryside to visit their friends when they realised they needed to stop for gas. The man was filling up the car when he _____ (2) (see) a penguin standing by a pump. He _____ (3) (think) it was very strange and when he went to the cashier to pay, he asked, 'why is there a penguin standing next to the pump?' The cashier replied, 'I don't know. It _____ (4) (be) there all morning.' The man replied.'Well, we can't leave it there, it's too dangerous. He might have an accident. What should I do?' The cashier suggested, 'you should take it to the zoo.' 'That's a good idea,' the man said. 'I _____ (5) (take) him now.' So the man and his wife put the penguin in the car and _____ (6) (drive) away. One week later, the man and his wife _____ (7) (return) to the same garage to fill up the car...and the penguin was still in the car. When the man went to pay, the cashier said to him, 'I thought you _____ (8) (take) the penguin to the zoo.' The man replied, 'we did. It had a really good time so tonight, we _____ (9) (take) him to a fish restaurant.'
The answer to (8) is given as took. Why it is not I thought you had taken, as it is a flash back it relates to the first part of the story?