Monosyllabic verbs end with stressed syllables, and there is only one consonant at the end, that is, they end with "a vowel letter+a consonant letter+a vowel letter", and the last consonant letter should be double-written before adding -ing.

Stop, stop.

But if the last letter is X, you don't have to write it again.

boxing

For polysyllabic words, if the last syllable is not stressed, but the following conditions are met, the last consonant letters should also be written in pairs.

It ends with the vowel letter+g.

Deceptive thing

Ending with vowel letters +l, m, you can write double or not.

Travel-Travel (British English) Travel (American English)