Today is Sunday. It's a sunny day. I'm in the park with my best friends Mary and Carol. There are many people in the park. They're doing different kinds of things. Some are walking by the lake. Some are talking under a big tree. Some are singing. Some are dancing on the playground. There are some kids playing tennis. Mary, Carol and I are sitting by the pool. It's really a fun day. The people here are all very happy. They're having a good time.

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小明制作了直接测量液体密度的“密度天平”。其制作过程和原理如下：如图甲所示，选择一个长杠杆，调节两边螺母使杠杆在水平位罝平衡；在左侧离支点10cm的位罝A用细线固定一个质量为110g、容积为50mL的容器。右侧用细线悬挂一质量为50g的钩码（细线的质量忽略不计）。

①调节杠杆平衡，往容器中加满待测液体，移动钩码使杠杆在水平位置平衡，在钩码悬挂位罝直接读出液体密度。

②当容器中没有液体时，钩码所在的位置即为“密度天平”的“零刻度”，“零刻度”距离支点O____cm。

③若测量某种液体的密度时，钩码在距离支点右侧31cm处，则此种液体的密度为____g/cm³。

④若此“密度天平“的量程不够大，可以采用____的方法增大量程（写出一种即可）。