Preheat oven to 400 degrees. Grease muffin cups or line with muffin liners and set aside.
Combine flour, sugar, salt and baking powder in a medium bowl. In another bowl, combine vegetable oil, egg and milk, and mix with a fork. Pour into the flour mixture and mix well. Add lemon juice. Fold in blueberries. Fill muffin cups to the top.
To make crumb topping, mix together sugar, flour, butter and cinnamon. Mix with fork and sprinkle over muffins before baking.
Bake for 20 to 25 minutes, or until a toothpick comes out clean.
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