28 as yet; so far; to date; up to date; up to now; up to the present

● 以上词组意为“到目前为止”，多用于现在完成时的句子中，用作状语。

● as yet位置较灵活。如：As yet, no man has set foot on Mars.（到目前为止，还没有人上火星。）We have known little as yet about the sun’s surface.（到目前为止，我们对太阳表面知道得很少。）The machine has worked well as yet.（这部机器至今一直正常运转。）Only twenty girls have come as yet.（到现在为止，只到了二十个女孩子。）

● so far多用于口语，有时可与as yet换用。如：Everything is in order so far.（到目前为止，一切正常。）So far, no man has traveled farther than the moon, but spaceships without people have reached other parts of the universe.（到目前为止，还没有人到月球以外旅行，但无人宇宙飞船已到达宇宙的其他部分。）So far everything concerned with the project has gone smoothly.（迄今为止，有关那项工作的一切都进展顺利。）So far, so good.（到目前为止，一切都很好。）

● to date, up to date; up to now; up to the present都有“至今”之意，可以互换。如：To date this question is without a definite answer.（这个问题迄今还无确定答案。）This is his best book to date.（这是到目前为止他所写出的最好的书。）He has worked up to now.（他一直工作到现在。）I haven’t received any letter from him up to date.（直到现在我还没有接到他的信。）We have not got any news from him up to the present.（直到现在我们还没得到他的任何消息。）Up to the present, the waters of all the Siberian rivers flow into the Arctic Ocean.（到现在为止，西伯利亚的河流都流入北冰洋。）