a.小丫的工作很努力 这里的“努力”是副词（adv.）相当于 work hard。 b.你努力学习中文了吗？-我努力了。 这里的前一个“努力”也是副词（adv.），后一个是动词（v.），相当于 try

I agree with Benjamin. In addition,努力 can be used as noun ,like 我的努力没有白费 努力 means effort

Hello Rose , I think the second pattern is rather correct. 努力 is more of a verb meaning 'try hard' . 你努力学习中文吗？我努力了。 You tried learning Chinese hard? I tried This makes sense . Other examples: 他不努力工作 ( ta bu nuli gongzuo )= He doesn't work hard. 我会尽最大努力 ( wo hui jin zui da nuli )= I'll try my very best.