当事人约定由第三人向债权人履行债务的，第三人不履行债务，债务人应当向债权人承担违约责任。 ()
查看答案
It can be learned from the last paragraph that ______.
A. genetic tests for most of the diseases can be produced now
B. gene tests are only suitable for those who have a strong family history of disease
C. almost all diseases can be cured with the development of the gene testing
D. the writer is optimistic about the future of gene testing
Which of the following statements is true in the eyes of the writer？
Applications of television arc beneficial to big cities.
B. Applications of television are believed to be good activities.
C. Applications of television are restricted to television systems.
D. Applications of television do benefit to the mass entertainment field.
所有权的权利主体总是单一的，因为同一项财产上不能同时存在两个所有权。 ()
A. 正确
B. 错误
张山是一著名童星，收入丰厚，其父张海从其收人中拿出2万元，资助了生活困难的弟弟张洋(张山的叔叔)，此行为 ()
A. 有效
B. 无效
C. 效力待定’
D. 得到张山同意后有效
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