Who do I address my cover letter to?

I'm applying for a new job in a new field - something I haven't done in many years. I'm stuck about who to address my cover letter to.

The job posting says I'll be reporting to the President and CEO. But in the instructions about how to apply, it says to email my application to the Office Assistant. I want to address it to the CEO, but the application instructions have me a bit thrown.

BTW, it says no phone calls, so I can't call for clarification.

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