The following is an example of a globular protein:

Explanation

Haemoglobin folds into a compact soluble ball with hydrophilic residues outside, which is what lets it dissolve in the cytoplasm of a red cell and carry oxygen. Keratin and collagen are fibrous structural proteins, long and insoluble. Histones are globular too, which makes the last option arguable, but haemoglobin is the standard textbook example the paper is looking for.