动物细胞与植物细胞的结构不同,导致了它们有丝分裂的不同,这是因为植物细胞[ ]
A.有叶绿体和细胞壁
B.有细胞壁和液泡
C.有细胞壁,无中心体
D.有叶绿体和液泡
答案:C
Read and answer. (根据提示或答语补全句子)
1. — Where is the washroom?
— It's on the _______ floor. (第一层)
2. — _______ is the gym?
— It's over there.
3. — Is this your music room?
— Yes, it _______.
4. — Is that your computer room?
— No, it _______.
边长为a的正方形,处于有界磁场,如图所示,一束电子以不同的初速度从同一位置水平射入磁场后,分别从A处和C处射出,则初速度vA:vC=____;所经历的时间之比tA:tB=____。