Each of the 400 people received from their boss____ gift —“Who moved my cheese?”—____ best-seller in the US—to understand how to deal with changes in their lives and work.

A．the; 不填

B．a; a

C．a; 不填

D．the; a

一物块停在水中时，露出水面的体积为6×10^-6m³，它的总体积为8×10^-6m³，

求：（1）物块在水中所受的浮力为多大？

（2）物块的密度为多少？