excuse me...
I try to practice my TOEFL by doing some exercises and I get these confusing questions.
I hope you can help me correct my answer...

1. Recycling is a means of reducing the demand on nonrenewable resources ____ of preventing some problems of pollution and waste disposal.
(A) either
(B) and
(C) too
(D) both
my answer is D, but I'm not sure


2. Although gorillas have no natural enemies, male leaders typically attack all intruders, thereby allow females and the young to flee to safety
my answer is allow, maybe it should be they allow ?


3. Candles and oil-burning lamps remained the chief sources of artificial illumination when the middle of the nineteenth century, when kerosene lamps came into common use
my answer is when, maybe it should be during ?


4. Cosmogony is a term applied to the study of the origin and development of the universe as well as to the theories concerned its origin
my answer is concerned, maybe it should be concerning ?


5. Flint was a favored material of prehistoric humans, which used it to make tools and weapons, because it would chip into shapes with sharp edges
my answer is which, maybe it should be who?


6. The flamingo constructs a cylindrical mud nest for its egg, which both parents care for it
my answer is the, maybe it should be omitted ?


7. Many sedimentary rocks were deposited in the ocean contain the fossils that record much of Earth's history.
my answer is record, maybe it should be recorded ?


8. The far northern wilderness of Quebec has vast deposits of iron ore, ____ province's leading mineral products.
(A) where the
(B) are the
(C) which the
(D) one of the
my answer is D and I'm not sure about it


9. Sunspots are but one manifestation of solar activity related of the Sun's magnetic field
.
my answer is but, maybe it should be ......... i don't know


10. In the United States, the attorney general is a cabinet member in charge with the administration of the Department of Justice
my answer is administration, maybe it should be administrator ?


11. Vitamins A and C and most of the B vitamins are retain in foods that have been canned.
my answer is retain, maybe it should be retained ?


12. Velocity may be uniform, in which case both speed and direction remain constant, variable, in which case speed, direction, or both changes
my answer is changes , maybe it should be change ?


13. Canada began cultivation wheat intensively in 1910, which led to a demand for tools, machines, housing, and building supplies.
my answer is cultivation, maybe it should be cultivating ? or maybe housing is the answer ?


14. A telescope consists of a series of lenses and, often, mirrors capability of producing a magnified image and of collecting more light than the unaided eye .
my answer is the, maybe it should be omitted ?


I am sorry if I make any mistake by asking too many questions.
thanks in advance..

May God always bless you guys...