Final answer:
The idiom used in the sentence 'Cassie was sick of bending over backwards to entertain her nieces' means that Cassie was trying very hard to entertain her nieces. The idiom used in the sentence 'Bobby would have been playing ball until the cows came home if it hadn't been for Suzie dragging him home' means that Bobby would have continued playing ball for a long time. These idioms are common expressions understood figuratively.
Step-by-step explanation:
The idiom used in the sentence 'Cassie was sick of bending over backwards to entertain her nieces' means that Cassie was trying very hard to entertain her nieces. The literal definition of 'bending over backwards' makes no sense in this context. Instead, it figuratively expresses the idea of exerting great effort or going to great lengths to please or entertain someone.
A similar idiom in the sentence 'Bobby would have been playing ball until the cows came home if it hadn't been for Suzie dragging him home' means that Bobby would have continued playing ball for a long time. The literal concept of 'until the cows came home' does not make sense, but figuratively, it implies an extended period of time.
These idioms are common expressions in English that are understood figuratively rather than literally.
Learn more about Idioms in English