Polypropene is prepared with a Ziegler-Natta catalyst. In the isotactic form, with the main chain drawn in a planar zigzag,

1. Aall the methyl groups lie on the same side of the plane of the main chain
2. Bthe methyl groups alternate regularly on opposite sides of the plane
3. Cthe methyl groups are placed randomly on either side of the plane
4. Dthe methyl groups are all replaced by hydrogen atoms in the middle of the chain