Missing Letter

[system]

socks

[scobie]

costs

[system]

cysts

[system]

stays

[scobie]

stash

[system]

haste

[system]

those

[system]

these

[scobie]

sheet

[system]

sheep

[scobie]

heaps

[system]

leaps

[system]

shape

[scobie]

peels

[scobie]

sorry changed two letters. peach

[system]

aches

[scobie]

cheat

[system]

chart

[system]

heart

[system]

teach