The chief manager has decided to put _____ he thinks is energetic, clever and capable to the position of the leadership of the company.

A．whatever

B．whoever

C．whichever

D．whomever

下丘脑在人体生理调节过程中发挥着重要作用。请据下图回答问题（甲、乙、丙、丁为人体内某种结构或细胞，A，B，C为调节物质）：

在反射弧中，兴奋只能从突触前神经元传至突触后神经元，而不能逆向传递的原因是（）。