For users, microkernel technology promises (90) , compact and sophisticated operating systems that are typically (91) across a range of hardware platforms. These operating systems will be customizable to let users run multiple operating system and application "personalities" on top of a single microkernel (92) .

Microkernel based systems can provide this flexibility because the core operating system functions are (93) from the large number of utilities, features and extensions that are layered on top of them. As a result, updating and maintaining operating system is easier, since developers don’t have to modify the (94) every time they must acid a new feature.

（91）是（）

A. moveable

B. made

C. portable

D. use

遗嘱人在危急情况下，可以订立口头遗嘱，危急情况解除后，遗嘱人能够用书面或录音形式订立遗嘱的，所立的口头遗嘱（）。

A．无效 

B．继续有效 

C．部分有效 

D．由遗嘱人自己决定是否有效