First, think about these forms: "The chances are good that if it can happen somewhere else, it will", and "The possibility is good that ...". This one is less natural sounding, but still ok "The possibilities are good that...". You can understand what those examples mean because they're not leaving anything out. However, over time the phrase "the chances are good that" has degraded into "chances are (that)." Words have just been left out for whatever reason, over time, and native speakers have gotten used to hearing it that way and just understanding it. That degradation has not happened with the other two example phrases I showed. This is likely the root of your difficulty in answering this question, which is at best challenging and at worst slightly unfair since it's mixing one of these degraded conventional expressions in with other options that don't involve such an expression at all. For your side question, the only answer that would make sense to me would be the word "being".

"Chances are" is a fixed expression/idiom. Outside of the idiom, none of the words fit. https://en.wiktionary.org/wiki/chances_are Also, you are correct that it should be "being careful".