1, B going -> to go

intend +to + V 
2, B go -> gone

QKHT before
3, B will -> would

said thành câu tường thuật nên will phải đổi thành would
4, C studying  -> to study

decide +to +V 
5, A am -> were

 If S V2,ed, S would V
6, A will -> would

(said thành câu tường thuật will phải đổi thành would
7, C to -> in

result in nghĩa là dẫn đến
8, D  had had-> were having

đây là câu QKHT
9. B  pollute -> pollution

10, A  Has -> Have 

tom and susan ngôi thứ ba phải dùng have
11, A pollute  -> pollution 
12, B wants -> wanted

Câu TT lùi HTD -> QKD

Question 13, B 

=>
1. B -> to go (intend to V : dự định)
2. B -> gone (QKHT before QKĐ)
3. B -> would (said -> câu tường thuật, will -> would)
4. C -> to study (decide to V : quyết định)
5. A -> were (câu đk loại 2 If S V2/ed, S would V)
6. A -> would (said -> câu tường thuật, will -> would)
7. C -> in (result in : dẫn đến) 
8. D -> were having (QKĐ when QKTD)
9. B -> pollution (air pollution : ô nhiễm không khí)
10. A -> Have (Tom and Susan -> số nhiều -> dùng Have)
11. A -> pollution (water pollution : ô nhiễm nước)
12. B -> wanted (câu tường thuật, lùi thì HTĐ -> QKĐ)
13. B (họp qua video)