八木天线由（）个有源振子、一个反射振子和若干个引向振子组成。
A、一
B、二
C、三
D、四
参考答案：A
用括号内所给词的适当形式填空
1. You are the___________(one) boy to come to the club.
2. My___________(mother) birthday is August 8th.
3. We have___________(sixth) classes every day.
4. These are___________(Jim) new clothes.
5. My cousin is two years old. Today is her___________ (two) birthday.
6. They have___________( twenty) strawberries.
7. Today is November ___________ (thirty).
8. Today is my sister's ___________( twenty-nine) birthday.
9. Grace has___________( five) good Chinese friends.
简述食品干燥保藏的原理
