"我现在上高一"的英语怎样说?

I'm now in high school,Grade One.

在这里不可用senior,senior means 高中最后一年,美国是12年级,不知国内是几年级.
高中一年级可以这么说, I am a freshman in high school.
or I am in nineth grade.(九年级是美国高中的一年级)

Now I'm in Grade 1 of a senior high school.

At now,I am a Senior High school student who study in the first grade.

I am in grade one of high school now.

I am a Senior High school student who study in the first grade.