up till now是什么时态的标志词

　　Yet this system has worked pretty well up till now.

　　然而截止到目前，这些系统的功效还是很好的。

　　I think it should be relatively objective up till now.

　　目前为止，我觉得还是很客观的。

　　I still remember the scene very well up till now.

　　这情景我一直到现在还记得很清楚。

　　I think this is the best answer up till now.

　　我觉得这是目前为止最好的答案。

　　Up till now, however, there is not such a law in China.

　　然而，迄今为止，中国还没有一部反垄断的专门法律。