混凝土灌注桩桩身混凝土应()。对钻孔桩桩身混凝土应全部进行()。对桩身混凝土质量有疑问和设计有要求的桩,应采用()进行检测。
参考答案:均质、完整;无损检测;钻芯取样
A series of contests _____ being held among the high schools of this city.
[ ]
A. has
B. are
C. is
D. have
合同生效的要件有哪些?