Answer:
C. The weather is nice today rainy, wet and cold tomorrow.
Step-by-step explanation:
Run-on sentences are those types of sentences where two or more independent clauses or sentences are joined in one sentence improperly. So, instead of keeping them in separate sentences, they are joined in one sentence but without the use of an appropriate conjunction.
In the given sentences, the one with a run-on sentence is option C. This is because sentence C contains two independent clauses "the weather is nice today" and "rainy, wet and cold tomorrow". And when they are joined together, no appropriate or proper conjunction is used to make them into one sentence.
Sentence A is wrong as it contains just one independent clause.
Sentence B is wrong as it correctly uses "and" to join the two independent clauses.
Sentence D is wrong as it is just a single independent clause.
Thus, the correct answer is option C.