Respuesta:
Si es de con could/couldn't es así:
10 could
11 could
12 couln't
13 couldn't
14 could
15 could
16 couldn't
17 could
18 could
19 could
20 could
21 could
22 couldn't
23 couldn't
24 could
25 could
26 could no longer walk
27 couldn't
28 could
29 could
30 could
