1. With plant species ______ at an alarming rate, scientists are creating a global network of plant banks to store seeds.
A. disappeared B. to disappear C. disappearing D. disappear
2. All our work will have been accomplished by the time the contract ______.
A. signs B. has signed C. is signed D. was signed
3. Some metals are better conductors of electricity than others, _______ means that the former have atoms that contain more free electron than the latter.
A. that B. this C. which D. it
4. Evidence came up _______ specific speech sounds are recognized by babies as young as 6 months old.
A. what B. which C. that D. whose
5. For many women, losing weight and always keeping it off is ______.
A. awkward B. terrible C. tough D. stubborn