<span>D. They have to predict which strains of flu will become active months before the flu season begins.
The text states, "</span>Creating a flu vaccine is a bit of a guessing game, because the shots take months to manufacture. Each year in February, the World Health Organization (WHO) tries to predict<span> what viruses may be circulating the following winter, a process that can change as bugs mutate. " This supports the answer that a challenge for vaccine makers is determining which strain of the flu must be targeted in order to prevent its spread. </span>
Your answer will be ridiculous for people in the future
The answer is compound because it has two predicates and two subjects. But either one if it has two of something it is compound
