`1)` The bridge was built `100` years ago.

`->` S + was/were (not) + V2 + ... : câu bị động trong QKĐ

`2)` My grandparents have never had a television in their youth.

`->` S + have/has + never + V3 ... : ai chưa từng làm gì

`3)` The house with the red door belonged to my aunt.

`->` S + V-qk + ...

`->` belong to sb: thuộc về ai

`4)` Life now isn't as simple as life in the past.

`->` A + be (not) + as + adj/adv + as + B ... : A (không) bằng B

`5)` It was difficult to learn how to ride a bike.

`->` S + be + adj/adv ... : cái gì làm sao

`->` learn how to V-inf: học cách làm gì

`6)` They didn't have cars, so they walked everywhere.

`->` S + did (not) + V-inf ...

`->` clause `(1)`, so + clause `(2)`: vậy nên

`-`

@magnetic

`1.` The bridge was built 100 years ago.

`-` Bị động QKD : S + was/were + V-ed/c3 + ... + (by+O)

`2.` My grandparents didn't have a TV in their youth.

`-` QKD : 

`(+)` S + V-ed/c2

`(-)` S + didn't + V-inf

`3.` The house with the red door belonged to my aunt.

`-` belong to sb : thuộc về ai

`4.` Life now is not as simple as life in the past.

`-` So sánh bằng : S + tobe + as + adj + as + S2

`5.` It is difficult to learn how to ride a bike.

`-` It + tobe + adj + to V-inf : nó thế nào để làm gì

`-` how to V-inf : cách làm gì

`6.` They didn't have cars so they walked everywhere.

`-` S + V so S + V : cho nên

`-` Because S + V , S + V : bởi vì