【单选题】Bacteria are microscopic organisms which live on the surface of objects. They are one of the most ancient living things, which exist on this planet for nearly 4,000 million years. Do you know the size...
A.
Bacteria are as big as a pinhead.
B.
Bacteria can not be seen by an ordinary microscope.
C.
Bacteria are hard to see because they often live together.
D.
Bacteria are very small so they can only be measured in microns.
【简答题】C Scientists used to explore on the suce of the ocean. Now they are exploring below the suce, too. They want to know about ocean water and the plant and animal life deep in the ocean. In 1934 th...
【简答题】A line of diaphragm wall is driven 4m into a firm clay and retains, on one side, a 3m depth of sand on top of the clay. Water table is at the suce of the clay. The unit weight of the fill is 17kN/m...