Which four are true？（）
A. Has-a relationships should never be encapsulated.
B. Has-a relationships should be implemented using inheritance.
C. Has-a relationships can be implemented using instance variables.
D. Is-a relationships can be implemented using the extends keyword.
E. Is-a relationships can be implemented using the implements keyword.
F. An array or a collection can be used to implement a one-to-many has-a relationship.
G. The relationship between Movie and Actress is an example of an is-a relationship.
B细胞活化的辅助受体（）
A. BCR复合体
B. CD19/CD21/CD81/CD225
C. 协同刺激分子
D. C3d受体
E. BCR识别特异性抗原
船舶违反本条例和有关法律、行政法规规定的，海事管理机构应当责令限期改正；在规定期限内未能改正的，海事管理机构可以（）船舶离港或者限制船舶航行、停泊、作业。
A. 禁止
B. 扣留
C. A+B
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