pH计的定位和核对用的是

A．pH比供试品溶液低3个单位的标准缓冲液

B．pH比供试品溶液高3个单位的标准缓冲液

C．pH相差3个单位的两种标准缓冲液

D．与供试品pH接近的标准缓冲液

E．pH约相差3个单位且供试液的pH介于二者之间的两种标准缓冲液

I don't know if I _______ time tomorrow. If I _______ time, I will call you. [ ]

A. have, have

B. will have, will have

C. will have, have

D. have, will have