"Remembrance" by Walter De la Mare

(1)The sky was like a waterdrop
In shadow of a thorn,
Clear, tranquil, beautiful,
Dark, forlorn.

(5)Lightning along its margin ran;
A rumour of the sea
Rose in profundity and sank
Into infinity.

Lofty and few the elms, the stars
(10)In the vast boughs most bright;
I stood a dreamer in a dream
In the unstirring night.

What is the rhyme scheme of the poem?

ABBA
Free verse
AABB
ABAB
ABCB