be having to?? I found a sentence in an English book going like: 'I'm afraid I can't come to ther party, I am having dinner with some important clients'' Here, I learned 'am having' means he has already arranged dinner plans. Then, can I say 'I am having to have dinner with some important clients.' to emphasize that it was not my choice?

'Where' and 'when' as a conjunction Hi, guys. I always appreciate your help. My question today is about 'where' and 'when.' I'm watching 60 minutes and I heard it says 'This is not euthanasia, when a doctor gives a patient a lethal injection.' I've been watching many people use 'where' as to explain further like that sentence. I wonder if there is any difference between 'where' and 'when' in that usage. Thanks, have a nice day!

'A break' as a meaning of 'opportunity' I saw someone use 'a break' as a meaning of 'a lucky opportunity', and dictionaries also say so too. Ex) His break came when the policy unexpectedly changed. (When the policy changed, he could defect from his country easily.) I am wondering I can say like this: 'Winning a lottery was not the biggest break in my life.' 'Finding this website was a break for improving my English.' 'My second break came when I met her.' I am not sure if I get the picture. If I don't, could you explain a little bit, please?

A question about 'underestimate' Let's say, Luke took an exam and he finished the exam in 15 min. I had supposed he would have needed at least 30 min. Here is the question. Can I say that 'I underestimated how long it would take for him to finish the exam'? Or, should I say 'I overestimated'? Confusing since I underestimated his ability but my estimation(30 min) was not under 15 min.

seek vs seek of vs seek after? which preposition should i use after 'seek'? or nothing? If 2 or more are possible, are there different meanings?

choice of? choice for? When I say, 'the train is empty, so I have a broad choice for seats', is this right? or should I say 'choice of seats'? It seems trivial but confusing because grammarly says it is 'of', but my teacher says it is 'for'.