According to Barrett et al$.(2020)$ article in Nature Sustainability, the single most promising innovation to address the key challenges facing agri$-$food systems is:

a$.$

Green packaging

b$.$

Blockchain

c$.$

None. The point of the article is that any innovation, if well apply, will successfully address current challenges.

d$.$

Regenerative Agriculture

e$.$

Self$-$driving technology to help farmers

f$.$

The point of the article is to assemble multiple innovations to address challenges.