—Have you known Dr. Jackson for a long time?

—Yes, since she________ the Chinese Society.

A．has joined

B．joins

C．had joined

D．joined

科学实验操作的正确性、规范性是实验成败的关键，同时也反映了实验者的科学素养。下列示意图中，实验操作规范的是   [ ]

A．过滤      

B．倾倒液体        

C．量取35毫升液体    

D．稀释浓硫酸