[单项选择]
Seeing Red Means Danger Ahead
The color red often means danger and by paying attention, accidents can be prevented. In the future, the color red also may help
(51) danger at construction sites. Thanks to new work by engineers, bridge supports or
(52) kinds of materials could one day contain a color switching material. It will turn red
(53) a structure collapses or falls apart.
The secret
(54) the color switching material is a particular type of molecule. A molecule is a group of atoms held together by chemical bonds. Molecules come
(55) all shapes and sizes, and make up
(56) . You can see, touch Or feel. How a molecule behaves depends on
(57) kinds of atoms it contains, and how they’re held together.
When a polymer (聚合物) containing a color switching molecule called a mechanophore (机械响应性聚合物) which is about to break, it produce a
(58) When a polymer with mecha
A. results
B. rules
C. tools
D. methods
