Look out the traffic is moving fast.it's---dangerous ---cros

Look out the traffic is moving fast.it's___dangerous ___cross the street .A.very ,t o B.so ,that
C.too,to 这个题应该选什么?请说明理由,
但是 选C从语法的角度讲也说得通吧 有没有更有说服力的理由？