the choice from the drop-down of "strict" makes a lot more sense. There are cases where it could be either, but it would be much more likely to be strict, so that should be an acceptable choice.
I was marked wrong for translating nghiêm túc as strict despite strict being one of the possible translations from the drop down hint. This problem should be corrected.
Again and again strict to use serious in English could be somewhat rhetorical as in you must joking they can't possibly be serious
I think "nghiêm túc" in this sentence, translate into English should use "strict" "long face" and “agelast”... Because 他的樣子很嚴肅long face/請你嚴肅一點be serious/你爸媽（或者在問家規）嚴肅strict嗎？