1.What are three things that scientists in the early 1900s learned about polio that helped us to understand what
causes this disease how it spreads from person to person?

AYUDA PLS

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explanation:

explanation:

venn diagram is pictorial representation with of circles showing the relation between two finite sets or things. the intersection part of two circles conveys the relation present in between those sets or things.

here in the venn diagram of sand and salt two circles represent sand and salt. but the area falling under the intersection of these circle represents the mixture of sand and salt.

so, in a venn diagram the mixture will be placed in a middle that is in between the intersection of two circles.

the correct answer is:

a. formation of precipitation

answer:

technetium is the most reactive. this is followed by silver. the least reactive out of these three elements is strontium.