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Thanks ProfessorMaisie.
Preamble is a little confusing for me.
The extra words have to be treated the same.
Does it mean you add or remove a letter from extra words?
For 1a, you can take out A from extra word. For 8a, you can add B to extra word.
I am still trying to figure out 37a, 41a, 42a and 43a.