预应力钢材张拉按( )双重控制;
A.<TABLE cellSpacing=0 cellPadding=0 width="90%" border=0>
<TBODY>
<TR>
<TD vAlign=top>千斤顶的油压; </TD></TR></TBODY></TABLE>
B.<TABLE cellSpacing=0 cellPadding=0 width="90%" border=0>
<TBODY>
<TR>
<TD vAlign=top>预应力钢材伸长率; </TD></TR></TBODY></TABLE>
C.<TABLE cellSpacing=0 cellPadding=0 width="90%" border=0>
<TBODY>
<TR>
<TD vAlign=top>千斤顶的油压、预应力钢材伸长率;</TD></TR></TBODY></TABLE>