Analysis of test questions: Escherichia coli can produce a large amount of insulin for treating diabetes. It uses transgenic technology. When human insulin gene is injected into E.coli, E.coli can produce insulin. There are two reasons for choosing bacteria as the recipient cells of genetic engineering: first, bacteria reproduce quickly and genes are simple. Secondly, the required products can be obtained by large-scale propagation of bacteria in a short time.

A cell engineering: plant cell engineering: plant cell culture to produce drugs (shikonin), artificial seeds, plant somatic hybridization (Chinese cabbage-cabbage).

Animal cell engineering: cultivating animal cells to produce drugs (lymphatic factor), monoclonal antibodies, animal cell fusion, embryo segmentation transplantation and nuclear transplantation (Dolly sheep, test-tube baby). So a doesn't fit the question.

B genetic engineering: using microorganisms to produce genetically engineered drugs, insect-resistant cotton, DNA probes, gene diagnosis (sickle cell anemia, leukemia) and gene therapy, etc. So b fits the question.

C fermentation engineering: Corynebacterium glutamicum synthesizes glutamic acid, Brevibacterium flavum synthesizes lysine, and engineering bacteria ferment to produce drugs. So c doesn't fit the question.

D enzyme engineering: enzyme preparation (for treating diseases, processing and producing certain products, detecting and diagnosing nuclear water quality monitoring, used in other branches of bioengineering), so D does not meet the meaning of the question.