1. Write a function that accepts the name and grade of the student. Grade distribution should be the following: A: Score >=90 B: Score >=80 C: Score >=70 D: Score >=60 The function should return the following if called student_grade("John", 87) Output: The grade of John is B The program should also print congratulations if the student's grade is A student_grade("Laura", 90) Output: Congratulations! The grade of Laura is A 2. Write a function that calculates the square root of a number. The function should employ the ifelse function. If the value contained in x is negative it should return NA. 3. Select any 18 alphabets from English letters without repetition.