How do I graph quarterly data which appears in Excel with gaps between the
mon this, like the first, and second columns below (the third column is
monthly):

Do I have to clean the data first, or is there a trick?

579.836 721.12 567.86 117.45 95.398 23412
_ _ _ 120.08 _ 23913
_ _ _ 120.83 _ 25196
586.415 732.82 575.79 121.24 _ 34446
_ _ _ 121.7 _ 26057
_ _ _ 122.04 _ 31790
584.511 738.72 580.24 122.16 _ 28815
_ _ _ 122.27 _ 30638
_ _ _ 122.29 _ 15793
594.252 744.45 587.69 122.44 _ 22563
_ _ _ 122.28 _ 27764
_ _ _ 122.25 _ 24114
597.912 750.01 589.68 122.12 100 18023
_ _ _ 124.94 _ 22988
_ _ _ 125.24 _ 23650
602.364 743.68 590.22 125.24 _ 23919
_ _ _ 125.22 _ 24943
_ _ _ 125.27 _ 24158
614.051 748.56 593.71 125.15 _ 21822
_ _ _ 125.06 _ 31242
_ _ _ 125.21 _ 16168
620.186 753.08 595.89 125.17 _ 20747
_ _ _ 125.43 _ 25912
_ _ _ 125.41 _ 24793
622.375 754.77 600.05 125.35 102.623 22105