• c (l) am: The missing letter is 'l' to form clam.

Here are the completed words:

11.

• c (l) am: The missing letter is 'l' to form clam.
• fr (e) et: The missing letter is 'e' to form fret.

12.

• sa (m) ear: The missing letter is 'm' to form smear.
• ke (y) our: The missing letter is 'y' to form your.

13.

• sai (t) ate: The missing letter is 't' to form satiate.
• afrai (d) og: The missing letter is 'd' to form afraid.

14.

• com (b) ngine: The missing letter is 'b' to form combine.
• som (e) gg: The missing letter is 'e' to form some.

15.

• sai (o) rry: The missing letter is 'o' to form sorry.
• fai (r) ie: The letter 'r' is already provided to form fairy.

16.

• ad (h) ear: The missing letter is 'h' to form adhere.
• ba (b) ust: The letter 'b' is already provided to form bust.

17.

• scar (f) ish: The letter 'f' is already provided.
• chie (f) riend: The letter 'f' is already provided to form chief.

18.

• pra (i) es: The missing letter is 'i' to form praises.
• ma (r) east: The letter 'r' is already provided to form mare.

19.

• pla (y) ew: The missing letter is 'y' to form play new.
• ma (g) ext: The student wrote 'q', but the correct letter is 'g' to form magnet.

20.

• cla (l) ear: The missing letter is 'l' to form clear.
• mo (d) est: The letter 'd' is already provided to form modest.