Which is the best way to combine these two sentences?
Breathing all that dust was not good for people's health. Many people got sick.
a. Breathing all that dust was not good for people's health, and many got sick
or
b. Breathing all that dust was not good for people's health, because many people got sick.
B is the best choice.
Sorry, but B is not the best choice. Getting sick was not the cause of "breathing all that dust..."
So either use A or turn B around:
Many people got sick because breathing all that dust was not good for people's health.
Both options (a) and (b) are valid ways to combine the two sentences. The choice between the two depends on the intended meaning and the desired emphasis in the context of the larger paragraph or text.
Option (a), "Breathing all that dust was not good for people's health, and many got sick," uses the coordinating conjunction "and" to join the two independent clauses. This implies a close relationship between breathing dust and people getting sick, without explicitly stating a cause-and-effect relationship.
Option (b), "Breathing all that dust was not good for people's health, because many people got sick," uses the subordinating conjunction "because" to indicate a cause-and-effect relationship explicitly. This option is more explicit in suggesting that breathing dust directly led to people getting sick.
To choose between these options, consider the intended emphasis and clarity of the message you want to convey.