also for not all

Read the following passage and mark the letter A, B, C, or D to indicate the best option for each of the blanks.

From the seeds themselves to the machinery, fertilizers and pesticides - The Green Revolution regimen depend heavily on technology. One (17)________, however, depends much more on technology - organic farming. Many organic farmers use machinery, but (18) ________ chemical fertilizers or pesticides. (19) ________ chemical soil enrichers, they use animal manure and plant parts not used as food - natural, organic fertilizers that are clearly a renewable (20) ________. Organic farmers also use alternatives for pesticides; for example, they may rely (21) ________ natural predators of certain insect pests. Then, the need arises, they can buy the eggs and larvae of these natural predators and introduce them into their crop fields.

Điền câu 18