PT73 S2 LR - I *really* need some help with explanations on a couple LR questions on this test

Question 9 (weaken) - Answer is C, i picked A

Question 18 (flaw) - Answer is E, i picked A

Question 19 (weaken) - Answer is B, i picked E

Question 21 (mbt) - Answer is E, i picked B

Question 22 (strengthen) - Answer is A, i picked B

*REALLLLYY* need help as I am taking the December exam. Huge thanks to anyone who will help!