Here are some possible interpretations and answers:
* Do openers have to be at the beginning of a sentence? No, they can definitely be in the middle. An "opener" could refer to a word or phrase that begins a new thought or idea within a sentence. For example: "I went to the store, however, I didn't buy anything." "However" is an opener, but it's in the middle of the sentence.
* Can a sentence start in the middle of a thought? This depends on the context. Sometimes a sentence can start "in the middle" of a thought if it's part of a longer conversation or narrative. For example: "I'm really excited about the party, but I'm not sure if I can make it." The sentence starts with "but" and implies there's a previous thought.
* Can a sentence contain multiple "openers"? Yes! You can have several introductory phrases or clauses within a single sentence. For example: "Although I was tired, and it was raining, I decided to go for a walk."
To give you a more precise answer, please clarify what you mean by "opener." Are you thinking about specific types of words or phrases, or is there a particular example in mind?