We are just _____ calling you up _____ you come in.

A. about; when      B. on the point of; while

C. on the point of; when      D. on the point of; as

While _____ in the room, we were all very excited.

A. waited    B. waiting    C. to wait   D. wait

We have been _____ by all our friends since we settled in the new house.

A. called on     B. called at    C. called into    D. called for

研究發(fā)現(xiàn)，砷( As)可以富集在植物體內(nèi)，轉(zhuǎn)化為毒性很強(qiáng)的金屬有機(jī)物，影響水稻的株高、根長和干重；加P（與As原子結(jié)構(gòu)相似）處理后水稻莖葉和根中P含量增加、As含量相對(duì)減少，水稻生長加快，干重增加。對(duì)此現(xiàn)象的解釋不合理是           

A．As在水稻細(xì)胞內(nèi)富集，由細(xì)胞膜的結(jié)構(gòu)特點(diǎn)決定

B．As進(jìn)入水稻細(xì)胞，導(dǎo)致有關(guān)酶失去活性，影響細(xì)胞代謝

C．P影響As的吸收，與細(xì)胞膜上的載體種類和數(shù)量有關(guān)

D．P是構(gòu)成磷脂、核酸和ATP的重要元素，能促進(jìn)水稻生長發(fā)育

研究發(fā)現(xiàn)，砷( As)可以富集在植物體內(nèi)，轉(zhuǎn)化為毒性很強(qiáng)的金屬有機(jī)物，影響水稻的株高、根長和干重；加P（與As原子結(jié)構(gòu)相似）處理后水稻莖葉和根中P含量增加、As含量相對(duì)減少，水稻生長加快，干重增加。對(duì)此現(xiàn)象解釋不合理的是（    ）    

A．As在水稻細(xì)胞內(nèi)富集，由細(xì)胞膜的結(jié)構(gòu)特點(diǎn)決定

B．As進(jìn)入水稻細(xì)胞，導(dǎo)致有關(guān)酶失去活性，影響細(xì)胞代謝

C．P影響As的吸收，與細(xì)胞膜上的載體種類和數(shù)量有關(guān)

D．P是構(gòu)成磷脂、核酸和ATP的重要元素，能促進(jìn)水稻生長發(fā)育