高二英语题~~~~~~~~~1 He didn’t work hard,( )leads to his failurs

高二英语题~~~~~~~~~
1 He didn’t work hard,( )leads to his failurs in the exam
A it B what C which D that
2 Tom failed in the maths,( )made him sad
A it B that C which D Band C
3 I still remember the day( )I met our foreign teacher for the first time
A on which B which C that D on it
4 This is the person( )I am thinking
A / B whom C of whom D of that