下列有关动植物生殖、发育的叙述中,错误的是( )
A:受精的鸟卵中能够发育成胚胎的是胚盘
B:植物扦插、嫁接和组织培养的繁殖方式都是无性生殖
C:试管婴儿是指用人工方法让卵细胞和精子在体外受精,并在试管内发育而诞生的婴儿
D:蜜蜂群中的雄蜂是由未受精卵发育而来,是完全变态发育
芸豆、黄瓜、西红柿、海带、花生等都是餐桌上常吃的菜品,小明同学想获取它们的种子来种植,你认为他不可能得到的是( )
①蓝藻 ②酵母菌 ③草履虫 ④小球藻 ⑤水绵 ⑥根霉菌 ⑦葡萄球菌 ⑧链球菌.
More than 6000 children were expelled(开除)from US schools last year for bringng guns and bombs to school,the US Department of Education said on May 8. The department gave a report on the expulsions(开除)as saying handguns accounted for 58 per cent of the 6093 expulsions in 1996—97,against 7 per cent for rifles or shotguns and 35 per cent for other types of firearms. “The report is a clear sign that our nation’s public schools are cracking down(严惩)”on students who bring guns to school,“Education Secretary Richard Riey said in a statement.“We need to be tough-minded(坚强的)about keeping guns out of our schools and do everything to keep our children safe.” In March 1997,an 11-year-old boy and a 13-year-old using hand-guns and rifles shot dead four children and a teacher at a school in Jonesboro,Arkansas.In October,two were killed and seven wounded in a shooting at a Mississippi school.Two months later,a 14-year-old boy killed three high school students and wounded five in Daducab,Kentucky. “Most of the expulsions,56 per cent,were from high schools,which have students from about age 13,34 per cent were from junior high schools and 9 per cent were from elementary schools.”The report said.