Article in English: Look for one with firm, green leaves that have not turned yellow or brown. The skin on the fruit should be golden brown and firm to the touch. Smell the pineapple to see if it's ripe: it should emit sweet, heady smell indicating that you've chosen it at just the right time to start a new pineapple plant.  Make sure the pineapple isn't underripe. It needs to be ripe in order to produce another pineapple. Check to make sure the pineapple isn't too ripe by tugging a little at the leaves. If they come right off, the pineapple is too ripe to plant. Be gentle. Make sure the pineapple doesn't have scale insects around the base of the leaves. They look like small grayish black spots.

Summary in Vietnamese:
Mua một quả dứa tươi.