她的屁股很结实。

Her butt is ___firm.

这家法律公司提供优质的服务。

This law ___firm provides excellent services.

尽管压力很大，他仍然坚持自己的立场。

Under great pressure, he remained ___firm in his position.

这块面包太硬了，我咬不动。

This loaf of bread is too ___firm for me to bite into.