Selecting rows from one DataFrame depending on values from another

Question

Take two data frames

print(df1)

   A  B
0  a  1
1  a  3
2  a  5
3  b  7
4  b  9
5  c  11
6  c  13
7  c  15

print(df2)

   C  D
a  1  1
b  0  1
c  1  1