A:one needs to have profound knowledge
B:profound knowledge is important
C:profound knowledge is a must
D:it is required that one has profound knowledge
回顾课文,大显身手。
龙葵是一种重金属镉的超积累植物。盆栽试验表明,在镉污染水平为25mg/kg 条件下,龙葵茎及叶的镉含量都超过了100mg /kg 。可推测,龙葵根部细胞对镉离子的吸收方式为