单选题：根据以下材料，回答题When our restaurant business failed, we headed nor

根据以下材料，回答题
When our restaurant business failed, we headed north in a camping truck to Texas, hoping to have a“fresh start”. At the 21 of Palo Duro Canyon( 峡谷 )State Park, I 22 a job advertisement hiring park hosts.The position offered a 23 , permanent campsite in the park,and 24 , the hosts served as a link be-tween the park's guests and the rangers (护林人). It was the perfect solution : a rent-free place to reorganize our lives. We entered the park and I made an 25 for the following day.
The park was 26 , so it took us some time to find an available site. That evening, as we finished our dinner, my wife saw two large skunks (臭鼬)walking toward our table. We 27 climbed onto the table and,for the next four hours, waited for them to 28 our camp.
Having survived that night, we were 29 that everything else would be all right. The next day we met with the people who ran the park. They explained our30 and gave us a beautiful campsite.
That evening, 31 , we learned about the canyon 32 . They were strong and cold, rocking our little camping truck violently, and we lay 33 in the dark until the winds died away. 34 the weeks that followed,we learned to survive in our truck and 35 the little money my wife 36 by substitute teaching. Building a successful business and then losing it had left very little time for building a successful 37 . For a time after our business 38I thought I might lose my family as well.
Living in the tiny 39 with no television, we sat close together reading and talking. One evening,standing under a jeweled sky, I found myself 40 for all the hardships. We had walked the trails and climbed the canyon walls. We had become a family !
第21题答案是(  ) A．back
B．edge
C．centre
D．entrance