阅读下面短文， 从短文后各题所给的四个选项 （A、B、C、D ）中，选出可以填入空白处的最佳选项。
Jenna, a popular girl from Westwood Middle School, had graduated first in her class and was ready for new 1 in high school.
2, high school was different. In the first week, Jenna went to tryouts (选拔赛) for cheerleaders (拉拉队队员). She was competing against very talented girls, and she knew it would be 3 for her to be selected. Two hours later, the 4 read a list of the girls for a second tryout. Her heart 5 as the list ended without her name. Feeling 6, she walked home carrying her schoolbag full of homework.
Arriving home, she started with math. She had always been a good math student, but now she was 7. She moved on to English and history, and was 8 to find that she didn't have any trouble with those subjects. Feeling better, she decided not to 9 math for the time being.
The next day Jenna went to see Mrs. Biden about being on the school 10. Mrs. Biden wasn't as 11 as Jenna. “I'm sorry, but we have enough 12 for the newspaper already. Come back next year and we'll talk then.” Jenna smiled 13 and left. “Why is high school so 14?” she sighed.
Later in 15 class, Jenna devoted herself to figuring out the problems that had given her so much 16. By the end of class, she understood how to get them right. As she gathered her books, Jenna decided she'd continue to try to 17 her new school. She wasn't sure if she'd succeed, but she knew she had to 18. High school was just as her mom had said: “You will feel like a small fish in a big pond 19 a big fish in a small pond. The challenge is to become the 20 fish you can be.”
着与月球表面成一倾斜角的直线飞行，先加速运动，再匀速运动.探测器通过喷气而获得推动力。以下关于喷气方向的描述中正确的是（ ）