I want to write to Sam, but I don't know _____. [ ]

A. where is his e-mail address

B. where his e-mail address is

C. what place is his e-mail address

D. what his e-mail address is

目前效果肯定，易于推广应用的防龋方法是

A．中药牙膏刷牙

B．酶防龋

C．防龋涂料防龋

D．氟化物防龋

E．糖代用品防龋