A district officer argues: 'The medicines handed out at the clinic are free. Whatever is free costs nothing. So the medicines cost nothing, and the district need set aside no money for them.' The argument turns on using one word in two senses. Which of the following identifies the shift?

Medicines free at the counter are still bought, carried and stored by somebody, and it is the district that pays. The argument works only because 'free' begins as a statement about what the patient hands over and ends as a statement about what the medicines cost to supply. The other options name words that keep one steady sense throughout the three sentences.