In English, when a verb becomes a present participle (i.e., the "-ing" form), the usual rule is that if the verb ends with a consonant letter plus a vowel letter followed by a consonant letter (i.e., the CVC structure), then the last consonant letter needs to be double-written and then "-ing". For example, "run" becomes "running" and "stop" becomes "stopping".
However, there are some verbs that do not double write the last consonant letter when forming the present participle, despite conforming to the CVC structure. This is usually because the last consonant letter of these verbs is "x", "w", or "y", or because of historical pronunciation or spelling. For example, "open" becomes "opening" and "tr**el" becomes "tr**eling", although they both conform to the CVC structure, neither of them needs to double write the last consonant letter.
When it comes to the word "open" specifically, its present participle form is "opening", not "openning". This is because in English, the pronunciation and spelling of "open" is already conventional, and there is no need to double write "n" to form a present participle. Similarly, words like "plan" (planning) and "begin" (beginning) do not need to double write the last consonant letter.
In general, whether or not a verb needs to be double-written for the last consonant letter to become an immediate participle depends on the pronunciation, spelling, and historical evolution of the verb. Therefore, when learning English, it is better to grasp the correct form of individual verbs through memorization and practice, rather than simply relying on rules.
Materials** on the Internet.