so far

0I say it's B, but a grammarian will have to give you the official reason. I can rewrite the main thought of the sentence like this: 01font00They 01i00have not arrived02i00 at any clear understanding to date because they 01i00have not excavated02i00 enough tombs.02font0-

0 “So far” means “up to now”. Therefore, you cannot use the past participle after it. 0-

0 Exactly! So far tells you what tense is correct for the context. B is the correct answer. 0-

0 It's true that "so far" means "up to now", but the past participle "excavated" is used after it quite correctly.02br
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00 The present perfect tense (01i00have02i00 + past participle) is correct with "so far", but not the past perfect tense (01i00had02i00 + past participle).02br
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00 CJ0-

0If it is not right to use SO FAR with a PAST TENSE, what makes it justifiable for CALD (Cambridge Advanced Learner's Dictionary) writers to use it in their dictionary with PAST and PAST PERFECT, in the meaning of until then?02br
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01b01font00She 01b01font00gave02font02b00 us a brief

0That's interesting. "So far" (i.e. "thus far") + the past perfect seems ok to me. I wonder if it's another AmE/BrE difference.02br
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00MrP0-

0 So "so far" means both "until now" and "until then", I suppose?02br
00 Hmmm. It sounded a bit strange to me in that example sentence.02br
00I don't think it's an American thing either. 05002br
00 In the "resume of the project" example, I'm also a bit queasy unless the utterance is made very soon after the giving of the resume.02br
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0Hmm. I suppose I read it as an example of reportage-in-the-past, to add a little immediacy to the story. 02br
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00I remember once I had qualms about the use of "yet" in a past context, though everyone else thought it was fine. Maybe "past-context-so far-tolerance" also varies from speaker to speaker!02br
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00MrP0-

0Mmmmmm. 05002br
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00 Yes! That's it. It has to do with past-context-so-far tolerance!02br
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00Er, er, umm, I guess. 051010id3711id35