There are few Spelling Rules which should be followed in the formation of words.
Final a consonant:
1. For the one-syllable words ending in single vowel + single consonant, double the consonant before a suffix beginning with vowel.
Examples:
• beg + ed = begged
• run + ed =running
• rob + er = robber
• sad + est =saddest
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Are the sentences all grammatical?
What is the meaning of "Final a consonant"?
All the sentences are fine, yes.
The term "final consonant" means the consonant at the end of a word. (final = end)