What does Dr Hedden’s experiment in paragraph 4-5 indicate?

(单选题)______ of the money ______ spent recycling the rubbish. (单选题)The girl looked at the man angrily ______ was talking loudly (单选题)______ book on the desk is ______ useful one. (单选题)We can ask him when he ______. (单选题)Please wait for me ______ the corner ______ three o’clock. (单选题)The factory was built in a secret place, around ______ high (单选题)______ that she was going off to sleep, I asked if she’d lik (单选题)One of the important questions they had to consider was ____ (单选题)She is very important to us. We have been prepared to do ___ (单选题)She was a friendly teacher. She spoke to the students ______