Question

1. Why was the Eleven Cities Tour of 1963 the most difficult race?

2. Why was the Eleven Cities Tour in 1963 the most difficult race?

3. Why was the 1963 Eleven Cities Tour of 1963 the most difficult race?
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Do we have to use 'in' or 'of'? Are all the questions grammatical and the same?

Answer 1

1 and 2 are correct.

The year, 1963, should not be repeated in # 3.

You can say, "Why was the 1963 Eleven Cities Tour the most difficult race?"