Issue writing a loop

How do you replace this:

            Set txtImprov1 = wdDoc.ContentControls(10).Range
            Set txtImprov2 = wdDoc.ContentControls(11).Range
            Set txtImprov3 = wdDoc.ContentControls(12).Range
            Set txtImprov4 = wdDoc.ContentControls(13).Range
            Set txtImprov5 = wdDoc.ContentControls(14).Range
            Set txtImprov6 = wdDoc.ContentControls(15).Range
            Set txtImprov7 = wdDoc.ContentControls(16).Range
            Set txtImprov8 = wdDoc.ContentControls(17).Range
            Set txtImprov9 = wdDoc.ContentControls(18).Range
            Set txtImprov10 = wdDoc.ContentControls(19).Range
            Set txtImprov11 = wdDoc.ContentControls(20).Range
            Set txtImprov12 = wdDoc.ContentControls(21).Range

with a for loop. the txtimprov... are of the type word.range if that makes a difference. The only part I can't figure out is the numbers after txtImprov(n), I was thinking something like.

for i = 1 to 12
   Set txtImprov(i) = wdDoc.ContentControls(i+9).Range
next i

But I dont think that would work. Any ideas.