某建设单位与甲公司签订一份施工合同，约定由甲公司为某工程的施工总承包商。甲公司经过建设单位同意将其中的幕墙工程发包给乙公司。为赶进度，乙公司将其中一部分工程又发包给丙公司。对于前述施工合同的效力，下列表述正确的是( )。
A．甲和乙的合同有效，乙和丙的合同有效
B．甲和乙的合同有效，乙和丙的合同无效
C．甲和乙的合同无效，乙和丙的合同有效
D．甲和乙的合同无效，乙和丙的合同无效
参考答案：B
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| Look! The bus 1 at a small bus stop. A man 2 out of the window. He sees a woman. She is selling 3 . The man wants 4 a cake. But he doesn't want to go out because it is raining. The man sees a boy. The boy is 5 the window. "Come here, boy," the man says. "Do you know 6 the cake is?" "Twenty fen," the boy says. The man 7 the boy forty fen and asks him to buy two cakes. "One is for you and the other is for me," he says to the boy. After 8 minutes, the boy comes back. He 9 a cake. He gives the man twenty fen and says, "Sorry, there 10 only one cake left." | ||||
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