Mary Kim, CFA, practices in the established country of Oldasia as well as in the emerging country of Newasia. By regulation, Oldasia prohibits licensed investment advisors from trading in securities ahead of their clients. Newasia has no laws or regulations in this area. Mary Kim may:（）

A. trade ahead of her clients in Newasia only.

B. trade simultaneously with her clients in Newasia only, as long as she has made full disclosure to her clients that she reserves the right to do this.

C. not trade ahead of her clients in either country.

利用油管接箍数计算液面深度，在用平均油管长度计算公式L=N〃L_均中N表示（）。

A、液面深度

B、油管接箍数

C、平均油管长度

D、10个油管接箍数的距离，mm