This disease is surprisingly difficult to catch, as most people have a natural resistance to it.
这种病令人惊讶的难以患上，因为大多数人对它有一种先天的免疫力。
Eels are long and difficult to catch.
鳝鱼很长而且很难抓住。
Once you get behind in class, it's difficult to catch up.
一旦落后于班上的进度，就难以赶上。
Once you get behind in class, it's difficult to catch up.
一旦落后于班上的进度，就难以赶上。
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