请问这句英文中的learned behavior前面问什么没有冠词?

learned behavior
【心理学】习得行为 在这里 这个 learned behavior 是即可数也可以不可数.都对,例如
Sleep is a learned behavior,and getting into a routine helps the process.
睡眠是一种习得行为,养成习惯会有助于这一过程.
That was learned behavior for me.I knew how to work in the kitchen.
这对我来说是应该学的东西.我已知道如何在厨房里工作.