Doug was carrying two drinks before laura arrived at the party. while he was walking, he didn't see that laura was walking toward his direction. he tripped over his shoes, which were untied, and spilled both drinks all over laura's new shirt. she was surprised and speechless.

what tense are the words that are in bold?
a.
past imperfect tense
b.
past progressive
c.
simple past tense
d.
past perfect tense