Two plus Two?

What is two plus two? Here are the answers given by ten-year-old school pupils over the last six decades:

1960:
'Four, of course.'

1970:
'I think it's three but it's the method that counts.'

1980:
'Just a second while I get our my calculator.'

1990:
'Just a second while I open a window on my PC and double-click on the Calculator icon.'

2000:
'Just a second while I check the addition home page.'

2010:
'Just a second while I check with my friends on MXit.'