${1.}$ They began building this house 2 months ago.
→ They have built this house for 2 months.
⇒ S + started/began + to_V/V_ing + khoảng thời gian + ago: bắt đầu làm gì
+ in + mốc thời gian
= S + have / has + V3/ed + for + khoảng thời gian
since + mốc thời gian