What are the top five causes of the bicycle tyre flats you experience?

I've had a puncture on each of my last four rides.  Which made me wonder what causes the most bicycle tire punctures in various parts of the world.

* 1. Please rank the following from 1 to 6.
1 is the cause of most of the bicycle tire punctures you have experienced.
5 is the cause of least of the bicycle tire punctures you have experienced.

* 2. If something else is the main cause of bicycle tire punctures you have experienced, please type that into the text box below.

* 3. Where do you live?:

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