<html><body onmousedown="isKeyPressed(event)"><p>请单击文档中的某处。当 onmousedown 事件发生时，警报框会提示您是否按下了 ALT 键。</p><p><b>提示：</b>在单击文档之前，请尝试按住 ALT 键（在您的键盘上）。</p><script>function isKeyPressed(event) { if (event.altKey) { alert("The ALT key was pressed!"); } else { alert("The ALT key was NOT pressed!"); }}</script></body></html>