她正试着把一本书顶在头上保持平衡。

She was trying to ___balance a book on her head.

火烈鸟用一条腿优雅地保持着平衡。

The flamingo ___balanced gracefully on one leg.

把买的东西放在背包里比在自行车上保持平衡要安全。

It's safer to carry shopping in a backpack than to ___balance it on your bike.