______ (52)
A.During
B.When
C.Not until
D.Meanwhile

___________ (61)
A.inhabited
B.attended
C.crowded
D.visited

___________ (63)
A.round
B.pitch
C.course
D.court

___________ (65)
A.remaining
B.resting
C.upholding
D.leaving

___________ (66)
A.that
B.which
C.whose
D.what

___________ (68)
A.varying
B.unsteady
C.unsettled
D.altering

What is the main subject of the passage?
A.The effects of cloud seeding
B.The process by which snow crystals form
C.Developments in methods of increasing precipitation
D.The scientific contributions of Vincent Schaefer

After the cloud seeding operations of the late 1940s and the 1950s, the farmers and ranchers mentioned in the first paragraph probably felt
A.optimistic
B.disappointed
C.modest
D.triumphant

Which of the following can be inferred from the passage about the term “weather modification”?
A.It was first used by Vincent Schaefer.
B.It refers to only one type of cloud seeding.
C.It is not as old as the term cloud seeding.
D.It has been in use since at least 1946.

The pronoun “they” refers to
A.ice-forming nuclei
B.water droplets
C.airplanes
D.clouds