考试时他紧张地嚼着口香糖。
He nervously ___chewed his gum during the test.
小狗正开心地嚼着一根骨头。
The puppy is happily ___chewing on a bone.
他花了一整天时间来反复思考这个复杂的问题。
He spent the whole day ___chewing on this complicated problem.
