This is the core of the problem.
Kore ga sono mondai no kakushin de aru.
this (indicating an item near the speaker, the action of the speaker, or the current topic); this person (usu. indicating someone in one's in-group); now; here; I (me); certainly
indicates sentence subject (occasionally object); indicates possessive (esp. in literary expressions); but; however; still; and
that (something or someone distant from the speaker, close to the listener; actions of the listener, or ideas expressed or understood by the listener); the; um...; er...; uh...
question (e.g. on a test); problem; problem (e.g. societal, political); question; issue; subject (e.g. of research); case; matter; question (i.e. doubt); public discussion; controversy; trouble; problem; inconvenience; difficulty
indicates possessive; nominalizes verbs and adjectives; substitutes for "ga" in subordinate phrases; (at sentence-end, falling tone) indicates a confident conclusion; (at sentence-end) indicates emotional emphasis; (at sentence-end, rising tone) indicates question
core; heart (of the matter); point; crux; kernel
be; is; indicates past or completed action; indicates light imperative
a certain ...; some ...