Building a Cork Boat
 As a young boy, John Pollack dreamed of building a full-size boat made entirely of bottle corks. [A] At the age of thirty-four, Pollack sailed his dream down the Douro River in Portugal. It all began as Pollack is likely to point out (16), with a single cork.
 To amass the staggering number of corks needed to construct the boat, 165,231 in all, Pollack convinced the staff, of several restaurants (17) in Washington, DC, to donate discarded corks for his cause. [B] Pollack eventually received cork donations from a cork-importing company (18) based in Portugal.
 Constructing the boat introduced a challenge of another variety. Pollack finally (19) tried gluing the corks together to create stackable logs, but he soon realized that this strategy was too time-consuming. [C] He calculated that it would have taken him and one other person more then a year’s (20) worth of eight-hour days to glue all the corks needed for the boat.
 Piles of corks threatened to take over Pollack’s apartment (21) . He used a foam template to assemble a group of corks into a pretty interesting (22) shape. He then fastened each cluster of corks with multiple rubber bands and encased each cluster in fishnet. To bind clusters together and shaping (23) them into flexible columns proved to be both efficient and architecturally sound. Dozens of friends expedited this proper (24) process by volunteering to help with the construction of the boat.
 The completed cork boat, which resembled a Viking ship, was more impressive than Pollack had ever imagined. [D] In his childhood imagination, he had saw himself (25) floating the boat in his neighbor’s swimming pool. But at a length of twenty-two feet (26), Pollack’s masterpiece was best suited with (27) a grand voyage. In 2002, the company that (28) had donated thousands of corks to Pollack’s project sponsored the vessel’s launch in Portugal. There, during the boat’s successful journey on the Douro River, in the country of Portugal (29) , Pollack’s dream was fully realized.
21- Which choice most effectively introduces the paragraph?
A. NO CHANGE
B. Over the course of many months, Pollack con-vinced people to help.
C. Pollack was afraid that he would have to put his cork boat dream on hold.
D.After a series of trials, Pollack devised a workable strategy.