It sounds _____ the singing of rails.
It is in their ability to speak ______ humans ______ from animals.
Tom, look at your shirt! It requires ________.
I am concerned ____ it that I can’t concentrate ____ my work because of headache.
_____of danger in the street at night, she had to go home, with a friend_____ her.
—Jack is very clever and he studies hard as well.—It’s no ______ he always comes out first in the exams.