14. I have never been to the ballet before.

It is the first time I have been to the ballet before

15.John and Mary moved to Edinburgh twenty years ago

 It is twenty years since John and Mary last moved to Edinburgh

16.The police started looking for him two months ago

for two months now the police has been looking for him

17.I have never seen a dirtier -looking dog

this is the first time I have seen a dirtier -looking dog

18.Mary rang hour and hours ago

it is hours since Mary last rang

19.it is ages since Alan visited his parents

Alan hasn't visited his parents for ages

20.she started to learn Enghlish 8 years ago

It is 8 years since she last started to learn Enghlish

21.I have never seen such a beutiful building

It is the most beutiful building I have ever seen

`14`. It is the first time I have been to the ballet before

`→` It is the first time + (that) + S + have/has + Verb (PP)

`15`. It is twenty years since John and Mary last moved to Edinburgh

`→` it is... since S + V (Động từ V ở thì quá khứ đơn)

`16`. For two months now the police have been looking for him

`→` Hai tháng nay, cảnh sát đã tìm kiếm anh ta

`17`. This is the first time I have seen a dirtier-looking dog

`→` This is the first time + S + have/has + P2: Lần đầu làm gì

`→` S +have/has + never + P2 + before

`→` S+ have/has not + P2 + before

`18`. It is hours since Mary last rang

`→` it is... since S + V (Động từ V ở thì quá khứ đơn)

`19`. Alan hasn't visited his parents for ages

`→` S + hasn't/haven't + Ved/V3 + S

`20`. It is 8 years since she last started to learn English

`→` it is... since S + V (Động từ V ở thì quá khứ đơn)

`21`. It is the most beautiful building I have ever seen

`→` Đó là tòa nhà đẹp nhất mà tôi từng thấy