森林里有许多危险的野兽，我们必须小心。

There are many dangerous ___beasts in the forest, so we must be careful.

他总是欺负弱小，真是个野蛮的畜生。

He always bullies the weak—what a cruel ___beast.

这个数学题真是个难题，我花了两个小时才解出来。

This math problem is a real ___beast—it took me two hours to solve.