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We can see that letters are S, S, E, E, I, R.
Case 1: When all 4 letters are different. There is only one way where we select one each S, E, I, R.
Total number of 4 letter words which can be formed using these letters = 4! = 24.
Case 2: When all 2 letters are of 1 type and 2 letters are different.
Total number of ways in which 4 letter can be chosen = 2C1*3C2 = 6
Total number of 4 letter words which can be formed using these letters = 6 x 4!/2! = 72
Case 3: When all 2 letters are of 1 type and remaining 2 letters are of different another same type. There is only one way when we select
S, S, E, E.

We have considered all possible cases. Hence, total number of four letters of the word can be made = 24 + 72 + 6 = 102. Hence, option D
is the correct answer.