： ‌The selection of a gene delivery system depends on _________.‌A: the duration of gene expression required for therapeutic effect  B: the target cell C: the size of the piece of DNA to be used in the gene therapy      D: the membrane that surrounds cells 答案:  the duration of gene expression required for therapeutic effect ; the target cell; the size of the piece of DNA to be used in the gene therapy     构词法练习1、