Question

1. a. Tom has Lost his key. He can’t get into the house.
b. Tom lost his key yesterday. He couldn't get into the house

Answer 1

Answer: a. Since Tom has lost his key, he can't get into the house.

b. Tom couldn't get into his house because he lost his key yesterday.

Explanation:  a. 'Because' can also be used instead of 'since' here.