Nested "IF" statements under MS Excel

I was trying the other day to use conditional statements in Excel, but was getting an error message. I did not want write a VBA-code for a simple task.
I wanted to calculate the score of Exam 2 for a student who had perfect attendance, a score of 90 or above in homework assignments, and a score of 90 or above in Exam 1. My policy this semester is that such a student can skip exam 2.

How I solved the problem?

First, I wrote one single IF statement for condition 1, which is the score in exam 1 as follows,

=IF(D3>=90,D3,($E$54-25)*$E$55),

where D3 is the cell where the score of exam 1 is for student i, and the expression ($E$54-25)*$E$55 is an expression to calculate the score for an exam with 25 questions. I will note this expression as C.
Let me denote the first IF statement as X1.

Second, I added a second IF statement to X1 conditional on class attendance as follows,

=IF(Attendance!E2="YES",X1,C),

where Attendance! is the name of a sheet. Let me denote the second IF statement as X2.

Third, I added a third IF statement to X2 conditional on the assignment score as follows,

=IF(Assigment!C2>=90,X2,C).

In this way "IF" statements can be nested almost endlessly.
The key in nesting IF is to make sure that the structure of an IF statement is respected,

=IF(condition,command,clearance)

=IF(A>B,A,B), 

which means if A is greater than B, then A, else B.