A、Learning by trial and error. B、Making friends with suppliers. C、Finding a good partner. D、Opening chain stores. A短文中提到But the

It was the summer of 1965. DeLuca, then 17, visited Peter Buck, a family friend. Buck asked DeLuca about his plans for the future. "I’m going to college, but I need a way to pay for it." DeLuca recalls saying. "Buck said, ’you should open a sandwich shop’."
    That afternoon, they agreed to be partners. And they set a goal: to open 32 stores in ten years. After doing some research, Buck wrote a cheque for $1,000. DeLuca rented a storefront in Connecticut, and when they couldn’t cover their start-up costs, Buck kicked in another $1,000.
    But business didn’t go smoothly as they expected. DeLuca says, "After six months, we were doing poorly, but we didn’t know how badly, because we didn’t have any financial controls." All he and Buck knew was that their sales were lower than their costs.
    DeLuca was managing the store and going to the University of Bridgeport at the same time. Buck was working at his day job as a nuclear physicist in New York. They’d meet Monday evenings and brainstorm ideas for keeping the business running. "We convinced ourselves to open a second store. We figured we could tell the public. ’We are so successful that we are opening a second store.’" And they did — in the spring of 1966. Still, it was a lot of learning by trial and error.
    But the partners’ learn-as-you-go approach turned out to be their greatest strength. Every Friday, DeLuca would drive around and hand-deliver the cheques to pay their suppliers. "It probably took me two and a half hours and it wasn’t necessary, but as a result, the suppliers got to know me very well, and the personal relationships established really helped out," DeLuca says.
    And having a goal was also important. "There are so many problems that can get you down. You just have to keep working toward your goal," DeLuca adds. DeLuca ended up founding Subway Sandwich, the multimillion-dollar restaurant chain.
Questions 16 to 19 are based on the passage you have just heard.
16. What was DeLuca’s purpose in opening the first sandwich shop?
17. What can we learn about DeLuca and Buck’s first shop?
18. Why did DeLuca and Buck decide to open a second store?
19. What contributes most to their success according to the speaker?