the first compact microwave ovens were sold in 1960. everybody didn’t use them until
the 1980’s.
a. comma
b. and
c. or
d. but
e. because
which one would best suit the sentence structure

The first compact microwave ovens were sold in 1960, but everybody didn’t use them until the 1980’s.
But is used to connect the 2 sentence because the two sentences give contradicting ideas
Microwave oven was sold during 1960 however people did not use it until the 1980s.
According to the rule of world language, if two given sentences gives idea with contradiction, you use but, yet, however, etc.
For example:
=> I bought a power bank online but I did not received it.
 => I love sweets however too much is yucky.

The songs were performed with the singers' eyes closed so they could focus on the words and preserve every detail.

Correct porqsuenabien