保证高可靠的焊接强度，使焊料熔点降低的方法是掺入少量的（）。_爱下问搜题

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问题单项选择题

保证高可靠的焊接强度，使焊料熔点降低的方法是掺入少量的（）。

A.金

B.银

C.锌

D.铋

答案

参考答案：B

选择题

MacDonald who had spent much of his time _____ graduating from college backpacking round Europe,

decided last year to settle down. [ ]

A. when

B. while

C. since

D. before

单项选择题

Artificial flowers are used for scientific as Well as for decorative purposes. They are made from (51) of materials, such as wax and glass, so skillfully that they can scarcely be (52) from natural flowers. In making such models, painstaking skill and artistry are called for, (53) thorough knowledge of plant structure. The (54) of glass flowers in the Botanical Museum of Harvard University is the most famous in North America and is widely known (55) the scientific world. (56) , there are several thousand models in colored glass, the work of two artist naturalists, Leopold Blalschka and his son Rudolph.
The intention was to have the collection (57) at least one member of each flower family native to the United States. (58) it was never completed, it contains more than seven hundred species representing 164 families of flowering plants. (59) detail of these is accurately reproduced in color and structure. The models are (60) n locked cases as they are too valuable and fragile for classroom use.

A．sustained

B．maintained

C．kept

D．concealed