25. C (have met ⇒ met)

HTHT + since + QKĐ

QKĐ: S + V2/ed 

26. A (has bought ⇒ bought)

DHNB: yesterday (QKD)

S + V2/ed 

27. C (was ⇒ has been)

DHNB: since (HTHT)

S + has/have + V3/ed 

28. A (has finished ⇒ finished)

DHNB: last night (QKD)

S + V2/ed 

29. C (has been ⇒ was)

HTHT + since + QKĐ

S + was/were  : thì QKĐ

30. B (will take ⇒ would take)

S + told + O + (that) + S+ V (lùi thì)

will ⇒ would 

31. D (graduates ⇒ graduated)

S + told + O + (that) + S+ V (lùi thì)

TLĐ + after + HTĐ

will ⇒ would 

HTĐ ⇒ QKĐ

32. B (can't remember ⇒ couldn't remember)

S + said to + O + (that) + S+ V (lùi thì)

can ⇒ could 

33. C (must look after ⇒ must be looked after)

S + must be + V3/ed: bị động - modal verb

34. C (is often supported ⇒ are often supported)

S + am/is/are + V3/ed: bị động 

`color{orange}{~MiaMB~}`