Which meter scheme is used in these lines from Robert Browning's "Porphyria's Lover"?

The rain set early in to-night,

The sullen wind was soon awake,

It tore the elm-tops down for spite,

And did its worst to vex the lake:

A.

iambic pentameter

B.

iambic trimeter

C.

iambic tetrameter

D.

iambic dimeter