各种根都有根尖。 [ ]
√
We can never expect ________ bluer sky unless we create ________ less polluted world. [ ]
A. a; a
B. a; the
C. the; a
D. the; the
牙釉质牙骨质界正确的是
A.牙釉质和牙骨质端一端相接占10%B.牙釉质覆盖牙骨质少许占30%C.牙釉质覆盖牙骨质少许占60%D.牙骨质覆盖牙釉质少许占60%E.牙釉质和牙骨质分离占30%