现在分词作状语的区分感觉很难区分现在分词作状语表时间和它作伴随状语的情况，比如下面这些句子：⒈Following Tom

现在分词作状语的区分
感觉很难区分现在分词作状语表时间和它作伴随状语的情况，比如下面这些句子：
⒈Following Tom, we started to climb the mountain.
⒉Opening the drawer, he took out a box.
⒊Hearing the news, they all jumped with joy.
⒋Returning home, he began to do his homework.
书上说第1，2个句子属于现在分词作伴随状语的情况，而第3，4句属于现在分词作状语表时间，相当于一个时间状语从句的情况。我感觉都一样，无法理解？？求高手清楚地解答下！