Final answer:
The appropriate word to fill in the blank is 'ni' which means 'neither' in English.
Step-by-step explanation:
In the given sentence, the appropriate word to fill in the blank is ni.
The word ni means 'neither' in English and is used to express negation or to indicate that two or more things are not present or happening.
In this sentence, it is used to connect the words 'no estamos contentos' (we are not happy) and 'preocupados' (worried) to express that the person is neither happy nor worried.
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