Which of the following python lines calculates the standard deviation of variables exam1 and exam4 from a csv file called examscores that contains four variables: exam1, exam2, exam3, and exam4? (a)import pandas as pdscores = pd. read_csv('examscores. csv')print(std[['exam1','exam4']])( b)import pandas as pdscores = pd. read_csv('examscores. csv')print(scores[['exam1','exam4'] ].)import pandas as pdscores = pd. read_csv('examscores. csv')print(std[['exam1','exam4']].) import pandas as pdscores = pd. read_csv('examscores. csv')print(scores[['exam1']].

The option B calculates the standard deviation of variables Exam1 and Exam4.

Explanation:

First, let's write the first two lines correctly:

Now, let's analyse each option:

- The option A is incorrect

The expression std[['Exam1','Exam4']] is the incorrect part because in this case std is working as a variable and the std was not previously declared. So it will generate an error.

- The option C is incorrect

The expression std[['Exam1','Exam4']].scores() is incorrect because of two reasons: first, std is working as a variable and the std was not previously declared (as in option A), second, .scores() is working as a method and in this case, scores is the variable. So it will generate an error.

- The option D is incorrect

The expression [['Exam1']] is the incorrect part because it doesn't include the 'Exam4' and the problem is asking for the standard deviation of variables Exam1 and Exam4.

- The option B is CORRECT

The expression std[['Exam1','Exam4']] refers to the variables Exam1 and Exam4 from the total exams. As scores is a pandas variable and .std() is a method provided by pandas library, the expression .std() allows to get the deviation standard of the variables Exam1 and Exam4.

Thus, the option B calculates the standard deviation of variables Exam1 and Exam4.

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