He is ________ to buy _________ for his parents.

A．rich enough; enough present

B．enough rich; enough presents

C．rich enough; enough presents

D．enough rich; presents enough

某粒子用符号^A_ZMⁿ⁺表示，下列关于该粒子的叙述中，正确的是       （   ）

A．所含质子数为A—n

B．所含中子数为A—Z—n

C．所含电子数为Z+n

D．中子数—电子数=A—2Z+n