Sure, here are the correct forms of the verbs and words in parentheses, as well as the complete sentences and rewritten sentences:

40. Four years **is** long enough for a secondary student to make progress in studying.
41. What **were you doing** when we called you yesterday?
42. I think we should **reduce** our carbon footprint to have a better world to live.
43. If they **went** to the supermarkets in the big cities, they would buy some souvenirs.

Supply the correct form of the words in brackets:
44. It is **convenient** for people to travel in urban areas as there are many other means of transport.
45. The noise from the cities probably makes people feel **stressed**.
46. The farmers are happily **loading** plenty of fruit at the city market.

Make complete sentences, using the cues:
47. It becomes dark, I feel the cold.
48. My father does not know how to look after the garden.
49. My friends wonder what to play on the Net.

Rewrite each sentence beginning as shown so that the meaning stays the same:
50. The city is famous, it can attract the high number of tourists.
→ The city is famous for attracting a high number of tourists.
51. They were late for school because they missed the first train.
→ Because of missing the first train, they were late for school.
52. You can ring this number whenever there is any difficulty.
→ You can ring this number in case of any difficulty.