Which of these is an example of how engineers have contributed to society? A. Our current understanding of viruses
B. The seven-mile bridge that spans across the Gulf of Mexico to
connect two cities of the Florida Keys
C. Nomadic tribes traveling in search of food to hunt and gather
D. The theoretical mathematics describing the orbits of planets
around the sun

B.

Explanation:

One of the biggest examples of engineers' contribution to society is they link different communities together through transport infrastructure.

The seven-mile bridge was an engineering wonder. Seven Mile Bridge connects two cities of the Florida Keys that include Knight's Key and Little Duck Key and promotes the transportation of goods or several other services which was not possible at that time (1900s).

It is the longest bridge in the world and is constructed by using the “segmental” technique and engineers were acknowledged for their work.

Hence, the correct option is B.

  the   balanced   equation   for   reaction of   ca metal   with   o2 to   produce   cao   is as below

2 ca+ o2→ 2 cao2

  explanation

the reaction is   balanced     since the   number of atoms   in reactant side is   equal to   number of atoms   in   product side.   for   example   they   are 2   atom of   ca in   reactant   side   and   2   atoms of ca   in   the product side.

  the   process   is a   meet the   requirement   of   redox   reaction because :     calcium   is   oxidized   from   oxidation state 0   to 2+   while   oxygen   is reduced from   oxidation   state   0   to 2-

hydrocarbons are organic compounds that contain only hydrogens and carbons. they can be saturated (those which contain only carbon-carbon single bonds) or unsaturated (those which contain carbon-carbon double or triple bonds) in nature. hydrocarbons can undergo several reactions like substitution, elimination etc.  

on substituting one or more hydrogen atoms in hydrocarbon it results in the formation of haloalkane. as the halogen atoms are large compared to the carbon and hydrogen atoms, due to which the molecular weight increases and the bond become polar because of presence electronegative halogen atom and results in the increase in boiling point of the haloalkane.

thus, the correct option is (b) that is the boiling point of the new compound increases on substituting a hydrogen atom with a halogen in a hydrocarbon.