题目

From mom’s love, patience and understanding, I have learned what a huge responsibility ___ is to raise a child. A. that                  B. it              C. this               D. one   答案：B大豆根尖细胞所含的核酸中，含有碱基A、G、C、T的核苷酸种类共有 [　　] A．8B．7 C．5D．4