72．How did Tavella operate the wheelchair in the laboratory? (A)By controlling his muscles． (B)By talking to the machine． (C)By moving his hand． (D)By using his mind．

69．What can we learn about the middle class families from the text? (A)They blamed the government for the tuition increase． (B)Their income remained steady in the last decade． (C)They will try their best to send kids to college． (D)Their debts will be paid off within 25 years．