Which of the following uses of the preposition 'but is correct?
I am sure no one but he would do such a thing.
He does not seem to be interested in anything but play with toys.
I cannot but to admire the beauty of the mountain summit.
There is no alternative but to walk all the way home
-----the rise in unemployment in cities, more and more people continue to move to urban centres.
Its main purpose is to get you excited about science by doing it rather than simply learning about it. What does 'it' refer to?