In terms of numerical reference,

 e) about less than 20% (lines 17-18) – refers to the export share from Africa to China.

About, slacking to less than 20% of African exported wares find its way to China. That information was taken from the horse's mouth.

Resposta em L17-18, as quais contêm copia da resposta. A opcao d) tb parece correta, mas peca por generalizar as exportacoes para USA, enquanto que a passagem diz que 90% se refere a "energy and minerals".