Read the following passage and mark the letter A, B, C, or D to indicate the correct word or phrase that best fits each of the numbered blanks from 25 to 29.
Look at the sky at night. How many stars can you see? Astronomers say
that we can see about 2,500 stars with the (25) eye. But of course we
can see more if we use a pair of (26) or a telescope. In fact, we can see
billions of stars with a powerful telescope.​