Perhaps you should try some spelling variations:
greatest challenges » greatest challenge, treatment challenges, related challenges
1.1 greatest » 100 greatest, _ greatest, its greatest
facing among » making among, eating among, earning among
deng era » qing era, deal era, peng er
among di » among hiv, among idp, among _
nan yan » nan ya, wang yan, qian yan
ng era » 5g era, qing era
yang » lang, wang

You may be able to get more results by adjusting your search query.

• If you are trying to use Boolean operators, they must be ALL CAPS: ((nan yan) OR (yang di))((ng era) OR (deng era)) 1.1 greatest challenges facing among di ;~.
• Adding a wildcard symbol may retrieve word variants: ((nan yan) or (yang di))((ng era) or (deng era)) 1.1 greatest challenges facing among di ;*.