${14.}$ Minh said he didn't know where Nga was then.
→ câu gián tiếp dạng trần thuật: S + said (that) + S + V(lùi thì)
${18.}$ Their room was being cleaned at 8 o'clock last Sunday.
→ bị động QKTD: S + was/were (not) + being + V3/ed + (by+O) + time
${19.}$ He wasn't taken to the zoo last Sunday.
→ bị động QKĐ: S + was/were (not) + V3/ed + (by+O) + time
${21.}$ An interesting book was being read in my bedroom.
→ bị động HTTD: S + is/am/are (not) + being + V3/ed + (by+O) + time
${22.}$ This novel can be translated into French by Mr. Brown.
→ bị động dạng động từ khiếm khuyết: S + can/could/should/might/may ... (not) + be + V3/ed + (by+O) + time