这位作者在她的小说中频繁提及古典神话。

The author makes frequent ___reference to classical mythology in her novels.

他在会议期间小心翼翼地避免谈到财务困难。

He carefully avoided any ___reference to the financial difficulties during the meeting.

报告中对进一步研究的必要性有所涉及。

The report contains a passing ___reference to the need for further research.