she stamped out the letters 'SOS ' in the snow. 请问为什么是 stamp out,

问题描述:

she stamped out the letters 'SOS ' in the snow. 请问为什么是 stamp out,
如果直接she stamped the letters 'SOS ' in the snow,不可以吗,

stamp out 踩出(表明有结果)
stamp 踩(只表明动作,不见得有结果)
本句中SOS是能看到的结果,因此用stamp out.