Which among the following code snippets can be used to calculate the average marks of a student in $5$ subjects, and give grades according to the following rules:

If average $>90,$ then Grade $=$ A

If average $>80,$ then Grade $=$ B

If average $>70,$ then Grade $=$ C

If average $>60,$ then Grade $=$ D

If average $>50,$ then Grade $=$ E