【单选题】Depths in the routes (Malacca and Singapore Straits) vary between 20m and about 23m but there are many areas of sandwaves and depths are liable to change. The statement infers that .
A.
depths in Malacca and Singapore Straits are the same all the time
B.
depths in Malacca and Singapore Straits are stable
C.
depths in Malacca and Singapore Straits are invariable
D.
depths in Malacca and Singapore Straits are changeable