The sentences that use the word "sift" correctly are:
- Finally, they sift the poured concrete so that the sidewalk is flat and level.
- Michelle wanted to sift through the sand to find seashells.
- Before baking a cake, sift the flour to remove any lumps.
The sentence "Luisa took a sift of the soda and gave her approval of the taste." is incorrect because "sift" is not used appropriately here. The correct term in this context would be "sip" instead of "sift."