illness是可数还是不可数

Illness 在当病痛解释的时候是不可数的.例如:

Too much work and too little rest often lead to illness.
过量的工作和过少的休息会引起疾病.

Illness 在当各种不同类型疾病的时候是可数的.例如:

You can never imagine how many illnesses a dog can catch.
你无法想象狗狗可以得多少病.