Question

complete the text with the correct pair of words.
the biologist _ the slide under the microscope and _ began analyzing the cellular structure of the muscle tissue.

sit... then
set... then
set... than
sit... than

Explanation:

To solve this, we analyze the context and word meanings:

1. For the first blank, "set" means to place or position (the slide under the microscope), while "sit" is an action of a person resting. Since we're talking about the biologist's action with the slide, "set" is appropriate.
2. For the second blank, "then" is used to show sequence (after setting the slide, then analyzing), while "than" is used for comparisons. The context is sequential, so "then" is correct.

Answer:

set... then