英语中有now是什么时态

　　Now is a good time to buy a house.

　　现在买房子正是时候。

　　It's time to go now.

　　该走了。

　　I read much less now than I used to.

　　我现在看的书比过去少得多。

　　Do it now please ─ not in three hours' time.

　　请现在就干，而不是三个小时之后。

　　The conflict has now reached a new level of intensity.

　　冲突现在已经达到了新的激烈程度。