noun
DUBIOUS : Some of us did our teaching practice in the countryside.
GOOD : Some of us did our teaching practice in rural areas.
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Use countryside when you are thinking about the beauty or lifestyle of this type of area: 'We have to act now to save the countryside for future generations.' 'We enjoy walking in the countryside around Bristol.'
To refer to areas that do not have cities or towns, use rural/country areas : 'Housing tends to be more affordable in rural areas.'