填空What a wonderful time they are having___(攀登)the rocks!

climbing

climbing
可以理解成climbing the rocks is a wonderful time they are having.
climbing the rocks做主语，所以要用动名词形式。
they are having做wonderful time的定语，为定语从句，中间省略了that
climbing the rocks is a wonderful time that they are having.
然后把这句话倒装下变成了感叹句
What a wonderful time they are having climbing the rocks!

我错了 还是climbing
但是原因是 climbing the rocks 做 time的同位语
they are having修饰time

to climb
hzve time to do sth

呵呵。都说ING的啊。有点没把握啊。
我觉得应是不定式。they are having 作time定语，省略that。后接不定式，感觉对的。
仅供参考，高手见谅。