a masked virus的用法和样例：
- He wore a mask so that no one should recognize him.
- Such feelings tend to remain submerge beneath a mask of social politeness.
- Her sociable manner is really a mask for a very shy nature.
- He conceals his worries behind a mask of nonchalance.
- He tackled a masked intruder at his home.
- What do you say to a masked ball?