How to filter maximum results entries

I have a mysql table

table name 'results'

Reg.No  SubjectCode  Attempt  Grade  Marks
112108  CMIS 1113    1        D      17
112110  CMIS 1114    1        A      85
112119  CMIS 1114    1        D      18
112108  CMIS 1113    2        D+     25
112110  CMIS 1113    1        D+     25
112107  CMIS 1113    1        B      70
112108  CMIS 1113    3        C      40
112110  CMIS 1113    2        C      40
112119  CMIS 1114    2        C      42
112120  CMIS 1114    1        D      17

This is about students' results.

Students need at least a "C" (marks>40) to pass the subject.

Until pass, students can have several attempts.

But from the second attempt maximum grade they can get is "C"

So students who was unable to pass the subject in first attempt,used to have another try until they pass the subjects

So for final results sheet the highest result will be take into account in each subjects.(highest results is given by the highest marks)

So for example highest marks of 112108 for CMIS 1113 is 40.

So likewise I want to get the students results for ecch subjects(But always maximum marks will be take into account)

Actually my expected results table should be like this

Reg.No  SubjectCode  Attempt  Grade  Marks
112110  CMIS 1114    1        A      85
112107  CMIS 1113    1        B      70
112108  CMIS 1113    3        C      40
112110  CMIS 1113    2        C      40
112119  CMIS 1114    2        C      42
112120  CMIS 1114    1        D      17

So how can I retrieve these data using sql query?