Step 1: Interpreting the relationship between the sentences.
The first sentence states that the construction began on time.
The second sentence states that it was delayed because of bad weather.
This shows a contrast between starting on time and later being delayed.
Step 2: Evaluating the options.
(A) appropriately uses although to show contrast between the two ideas.
(B) uses since, which indicates cause and creates an illogical meaning.
(C) uses so, which suggests result and is incorrect in meaning.
(D) is grammatically incorrect and does not properly combine the sentences.
Step 3: Final Conclusion.
Accordingly, the correct answer is option (A), as it properly expresses contrast between the two statements.