String Sentence; String Str1, Str2, Str3, Str4;

Multiple Choice

String sentence;
String str1, str2, str3, str4;
Int length1;sentence = "First exam is on Monday.";str1 = sentence.substring(6, 12) ;
Str2 = str1.substring(0, 4) ;
Str3 = sentence.replace('i', '#') ;
Str4 = sentence.indexOf("on") ;length1 = sentence.length() ;Based on the code above, what is the value of str4?

A) 11
B) 12
C) 13
D) 14