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Yes: merely being lower isn't enough to guarantee visibility, because another intermediate tower might be (lower than the tallest but still) tall enough to block it. Like this, if I can get the formatting to work:
You can't see the third tower from the first, because the second is in the way.
Yes, exactly so.
There is another small ambiguity here. The towers 2, 3, and 4 have colinear tops. But this is the only case and not important for the solution.