Which poetic technique does robert browning use in this excerpt from “my last duchess”?

"of joy into the duchess' cheek: perhaps
frà pandolf chanced to say "her mantle laps
over my lady's wrist too much," or "paint
must never hope to reproduce the faint
half-flush that dies along her throat: " such stuff
was courtesy, she thought, and cause enough
for calling up that spot of joy. she had
a heart—how shall i say? —too soon made glad,"

a) enjambment
b) blank verse
c) open form
d) end-stopped lines