This is done to find the relationship between 2 variables. One dependent and one independent.
When to use Multiple regression test?
Extension of regression test. It is used to predict value of 1 variable when it depends on 2-3 other variables. Multivariable, basically.
When to use 1-sided t-test?
We check for possibility of relationship of something from one side. 1 side effect. With a hypothesis and its alternate.
When to use 2-sided t-test?
This is same as 1-tailed but it looks for possibility from 2sides. A hypothesis and alternate, whether less or more.
Now, Options A and B are not right since we aren't comparing 2 variables here. People believe second born subjects are more intelligent. We have to perform a test to see whether this is true or not. One sided answer. So, we will use One-sided t-test.
the number before n is the difference (what it goes up in), and the second is the ‘zeroth’ term: you take away the 2 you got from the first value, 3, and get 1 :)
and down is rounded to 
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and up is going closer to 