From the journal "Successes of Physical Sciences" Vol. 169, No. 4 for April 1999. , 419-441 s. Almost 30 years ago, an article by the author with the same title was published. Its main goal, largely of an educational nature, was to expand the horizon of young physicists. To do this, a list of issues that seem particularly important and interesting was compiled and commented on .. Of course, any such list is subjective and incomplete, but one cannot embrace the vast and some limitation of the list is inevitable. The author has several times supplemented the list and explanations to it .. This article pursues the same goal as before, but taking into account the situation at the end of the 20th century.