Read this prompt.

create a multimedia presentation claiming that teaching children more than one language is beneficial to their brain development. use research and evidence to support your opinion. use persuasive techniques and a variety of visual aids in your presentation.

which statement provides the best support for this claim?

many middle schools and high schools offer multiple foreign-language classes.
learning a second language is extremely challenging for most people.
speaking multiple languages improves comprehension and problem-solving skills.
careers in language interpretation are in demand around the world.

The correct answer is: Speaking multiple languages improves comprehension and problem-solving skills.

Indeed, as a former multilingual professional interpreter I can vouch to that fact, which has also been proven by scientific research.  When you learn a new language you are confronted by different grammatical structures, different semantics, different tonalities and above all the vast richness of a foreign culture (in both its negative and positive aspects).

Those intrinsic characteristics are both challenges to overcome and opportunities to learn and they require the use of a myriad of methods, improvisations, work and intense mental activity that inevitably enhances the cognitive capabilities of the learner in terms not only of memory but of thought processes and even emotional adaptation.  

Being confronted to such an enriching complexity inexorably leads the learner to apply all that acquired knowledge and mental acuity to all fields and situations of his normal life. This means that he/she will be able to comprehend knowledge faster and more efficiently solve problems.

The other assertions are arguable, or even incorrect:

Careers in language interpretation are in demand around the world. (That might change in the not so distant future with the use of automated translation/interpretation systems which keep getting better and better and with the rise of multilingualism).

Many middle schools and high schools offer multiple foreign-language classes. (This has little or no influence upon the claim of the question).

Learning a second language is extremely challenging for most people. This has little or no influence upon the claim of the question and would actually be considered a negative aspect of the phenomenon).

adverb is the answer i believe.

what are the words supposed to be listed?