The rockers contact the floor at only two points, giving the occupant the ability to rock back and forth by shifting their weight or pushing lightly with their feet.
请问老师:
1 giving现在分词短语是做状语吗?那逻辑主语是什么呢?
2 to rock back and forth by shifting their weight or pushing lightly with their feet 这个不定式短语是做定语修饰 the ability吗?