芹菜发生空心现象，在同一植株上是内叶先于外叶。
参考答案：错
GB1103-2007规定，棉花按色特征分为（）类型。
A.白棉
B.灰棉
C.淡黄染棉
D.黄染棉
The difference between international and national Navtex Service is limited to（）.
A.frequency allocated
B.both language and frequency
C.language used
D.transmission power and time
