请观察下列句子,注意主语从句的用法,找出主语从句的连接词。 1.That the earth travels round the sun is a well-known fact. 2. It is uncertain whether the artist can do it or not. 3. Who will act the lead in the play has not been decided yet. 4. Where the young man has gone is not known. 5. It is not yet decided when and where the test will be given.