Read the poem. The Courage That My Mother Had

by Edna St. Vincent Millay.

The courage that my mother had
Went with her, and is with her still:
Rock from New England quarried;
Now granite in a granite hill.

The golden brooch my mother wore
She left behind for me to wear;
I have no thing I treasure more:
Yet, it is something I could spare.

Oh, if instead she’d left to me
The thing she took into the grave!—
That courage like a rock, which she
Has no more need of, and I have.

In "The Courage That My Mother Had," what does the phrase That courage like a rock tell readers about the speaker's mother?

A: She protects the speaker from harm.

B: She is strict and inflexible.

C: Her bravery and strength is unwavering.

D: Her personality is difficult to relate to.