Subordinate clauses that are not for comparison - should we use が or は？


In a subordinate clause, が is often used.

However, some sentences with けど or のに are used with は because they are for
comparison.

But it seems to me that some sentences with けど or のに are not for comparison.

In those cases, do we use が or は?

**Example 1**

> 先生（が/は）答えを教えたけど、弟は低い点数を取った。

> My younger brother got a bad grade although the teacher had told him the
> answers.

**Example 2**

> 彼氏（が/は）プレゼントを買って置いたけど、彼女の弟はそのプレゼントを隠した。

> Although the boyfriend had bought a present and put it there, the
> girlfriend's younger brother hid it away.

**Example 3**

> 先生（が/は）答えを教えたのに、弟は低い点数を取った。

> My younger brother got a bad grade even though the teacher had told him the
> answers.




I do feel contrastive sense when は is used in those sentences. That is, with
は, each sentence sounds somewhat like "On one hand, A did blah-blah, however
B..." and there is a contrast between A's action and B's action. In other
words, the subordinate clause will be more emphasized. Both が and は are
natural, though.




I do feel contrastive sense when は is used in those sentences. That is, with
は, each sentence sounds somewhat like "On one hand, A did blah-blah, however
B..." and there is a contrast between A's action and B's action. In other
words, the subordinate clause will be more emphasized. Both が and は are
natural, though.

