Double
Double a:
aa.
Double b:
bb.
Double c:
cc.
Double d:
dd.
Double e:
ee.
Double f:
ff.
Double g:
gg.
Double h:
hh.
Double i:
ii.
Double j:
jj.
Double k:
kk.
Double l:
ll.
Double m:
mm.
Double n:
nn.
Double o:
oo.
Double p:
pp.
Double q:
qq.
Double r:
rr.
Double s:
ss.
Double t:
tt.
Double u:
uu.
Double v:
vv.
Attention! It's 'w' (double-u)
https://en.oxforddictionaries.com/explore/why-is-w-pronounced-double-u.
Double w (
double double-u):
ww.
Double x:
xx.
Double y:
yy.
Double z:
zz.
Examples
1) L, e, double t, e, r = letter.
2) B, double o, k = book.
3) L, double e, k = leek.
4) S, p, a, double r, o, w = sparrow.
5) A, double c, e, p, t = accept.