杨树茎内形成层细胞经过细胞分裂，向内、外分别产生 _____和 ______ 。
木质部；韧皮部
You have been in a new school for months and have made new friends and met new teachers. Describe one of them who gives you the most unforgetable impression and using your experience ,explain why and how. Limit your writing to about 120 words.
