Explanation:
To combine two contrasting ideas, we use the conjunction "but". The conjunction "but" is used to show a contrast or contradiction between two ideas or statements. It is used when there is a difference or opposition between the information being presented.

Example:
- I wanted to go to the party, but I had to study for my exam.
- The weather was hot, but we still enjoyed our picnic.

In both examples, there is a contrast between the first part of the sentence and the second part. The conjunction "but" is used to connect these two contrasting ideas.

Other Conjunctions:
While the conjunction "but" is used for contrasting ideas, there are other conjunctions that serve different purposes:

- "And" is used to connect similar or related ideas. It is used when the information being presented is in agreement or addition.

Example: I went to the store and bought some groceries.

- "Or" is used to present alternatives or choices. It is used when there is a selection between two or more options.

Example: Would you like tea or coffee?

- "Since" is used to indicate a cause and effect relationship or a reason. It is used when the information being presented is explaining why something happened or is happening.

Example: I couldn't attend the party since I was feeling unwell.

Therefore, when combining two contrasting ideas, the conjunction "but" is the most appropriate choice.