Designing Cisco Network Service Architectures (ARCH) (#1)

Which route summarization most efficiently reduces perceived network complexity that is composed of subnetworks ranging from 172.16.20.0/24 to 172.16.36.0/24?

172.16.8.0/21
172.16.8.0/19
172.16.20.0/20
172.16.0.0/18
172.16.20.0/19