Here are the correct forms of the verbs in brackets:

41. My house **is being built** at present.
42. We would rather **stay** at home than go out on rainy days.
43. Yesterday, when we **visited** them, they **were having** dinner.
44. The weather is terrible today. If the weather **is** good, I **will go** for a walk.
45. I **wrote** to my pen pal 2 months ago, but I **have not received** his reply since then.
46. All the candidates **were selected** for a second interview.
47. The wallet **found** on the street was handed in to the police.
48. The girl over there **chatting** on the phone is the new secretary.
49. The last person to **leave** the room must turn off the lights.
50. The young boy **playing** with the yoyo is my brother.