用所给动词的适当形式填写下面的句子并体会它们的共同特征。
1. Having worked(work)hard all day, I went to bed early.
2. Having collected(collect)special clothes from the observatory, we put them on before we went any closer.
3. Looking (look)carefully at the ground, I made my way to the edge of the crater.
4. Having studied (study) volcanoes for many years, I am still amazed at their beauty.
