demonstration可數嗎

　　We were given a brief demonstration of the computer's functions.

　　有人向我們簡短演示了這種計算機的各種功能。

　　The police were much in evidence at today's demonstration.

　　在今天的示威集會上警察隨處可見。

　　She walked me through a demonstration of the software.

　　她一步步地給我演示軟件。

　　There was a strong police presence at the demonstration.

　　示威現場有了大批警察。

　　The police are preparing themselves for trouble at the demonstration.

　　警察正在準備防范示威時可能出現的騷亂。