Daisywheel printers were very common a few years ago. They used a sort of wheel with solid characters which rotated and hammered against the ribbon, but they couldn’t print pictures or diagrams, and were very slow and noisy. The word 'which' refers to __________.
เลือกคำตอบเดียว
a. solid characters
b. a sort of wheel with solid characters
c. wheel with solid
d. a sort of wheel