The astronauts found that ______ the spaceship went further and further into space, it became more and more difficult to control its own movements.

A．if

B．till

C．as

D．while

在营销的产品策略中，就整体产品而言，产品的质量、款式，特点属于产品的( )。

A．核心含义
B．形式含义
C．延伸含义
D．功能含义