r6 vs r7
......
1616
* take-took-taken
1717
* write-wrote-written
1818
* see-saw-seen
19
* am(is, are)-was(were)-been
19
* be(am, is, are)-was/were-been
2020
* think-thought-thought
2121
* rarena-rarena-rarena
2222
* come-came-come
......