Which parts exactly are we supposed to cover with the mention in queries

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Utterance&Annotation in the guideline:

1.number of countries in europe: knowledge:display -- [number of countries in europe]<search_phrase>
2.what is the most common problem for two thousand four toyota matrixes: knowledge:automotive -- [what is the most common problem for two thousand four toyota matrixes]<search_phrase>

Question:

This two examples above are driving us confused when we are dealing with some queries. As we all know, in some queries, the query only makes sense as a searchphrase as a whole, like "how tall was steve jobs", since there's no way to throw away the "how tall was" part and have a somewhat same search result. But in others things can be a lot different. For example, "what is the most common problem for two thousand four toyota matrixes" as a search phrase might just give you the same result as "most common problem for two thousand four toyota matrixes". We are eager for a rule of thumb to determine which parts exactly are we supposed to cover with the <searchphase> mention in a query when there are "redundunt" parts that seem can be excluded from the mention.