Nothing tricky about this one. A role or profession in the singular requires an article: “he is a teacher” or “she is the CFO”.
“I had a phone conversation with ten dentists” in English is a conference call, but in Dutch it would usually mean ten separate calls, one with each.
The plural of person is ‘people’, except in legalese and occasional old-fashioned texts.
There’s no such thing as “a training”. You either receive training – a general, uncountable noun – or take a training course.
Singular subjects require singular verbs and plural subjects require plural verbs… except when they don’t.
Um… surely not. The Dutch don’t make mistakes when referring to their own country, do they? It turns out to be a surprisingly tricky one.
A singular noun. Yes, the origin of the word is the Latin plural of datum, but that’s not the point. Languages are dynamic and changing; if you don’t go with the flow, it can sound hypercorrect.
The word “and” creates a plural in English – in this example, you’re talking about more than one century, after all.