If your choices are the following:
a. The flu and the common cold are caused by viruses.
b. Viruses are passed by contact between people.
c. Cold and flu season occurs when the weather is cold, so there must be a connection.
d. All of the above excerpts are biased.
Then the statement that is considered to be biased is c. Cold and flu season occurs when the weather is cold, so there must be a connection.