我们每周有六节科学课。

We have six ___periods of science a week.

下课后，铃响时，我留在教室里问了一些问题，我的新老师给了我一些解释。

After the ___period, when the bell rang, I stayed in the class to ask some questions and my new teacher gave me some explanations.

下一节课是数学。

The next ___period is mathematics.