Write the next sentence in this paragraph:

How to fold a plastic bag
Flatten the bag.
Make sure to line up the sides of the bag so that the handles are parallel to each other. Pay attention to the way you orient the handles, as they play an important role in the folded triangle's structure.

Available choices:
a). This step should not be carried out with flat bags; rather, it needs to be done by hand on a flat surface. Ideally, position the bags so that the bottoms of each bag line up with the bottom and sides of the bag.
b). Finish folding, then attach the lid. A lid will keep the wrapped wrapping paper from sticking together.
c). Because the plastic bags can fall apart, make sure that they match up properly. While folding the bag at a 90-degree angle is important, it is also important to make sure that it stays relatively flat when it rests.
d). This is easiest to do on a hard, flat surface like your kitchen counter. If you're especially dexterous, you can try folding a triangle in the air without a flat surface.
d).