Level 1

s, a, t, i, p, n

Level 2

ck, e, h, r, m, d

Level 3

g, o, u, l, f, b

Level 4

ai, j, oa, ie, ee, or

Level 5

z, w, ng, v, oo

Level 6

y, x, ch, sh, th

Level 7

qu, ou, oi, ue, er, ar