Sentence Correction

Bricolage is an unusual art form because it is formed of materials such as knickknacks and cast-offs not usually employed by fine artists.

1. because it is formed of materials such as knickknacks and cast-offs
2. because it is formed of materials like knickknacks and cast-offs that are
3. because it is formed of materials like, knickknacks and cast-offs, materials
4. in that its formation, materials such as knickknacks and cast-offs, is
5. in that it is formed of materials such as knickkacks and cast-offs, materials

I correct answer is shown as E but I feel E is quite wordy and unsuitable to be the correct answer choice. A sounds just fine!
Please explain.

Thanks
Source: Princeton Review Practice Test 10