'while' - is it ambiguous to indicate a contrast?

Rhetorical  construction;   Logical  predication
    This sentence compares percentages and uses the  prepositional phrases in France and in Germany to distinguish the percentage  of energy in each country coming from nuclear power.  This information is most efficiently and clearly presented in two clauses  joined by the conjunction whereas, which signifies a difference between the  situations in the two countries. Each clause must identify what the  percentage refers to—that is, the portion of the respective country's energy  that comes from nuclear power.
   
    A    While is somewhat ambiguous, since it might indicate  simultaneity rather than contrast; the referent of it is ambiguous, raising  questions about just what two things are being compared.
    B    This sentence compares 75  percent to Germany; it is not clear what 33 percent refers to.
    C    Correct. The two clauses joined  by whereas indicate clearly that the comparison is  between the different percentages of energy coming from nuclear power.
    D    The use of the definite article  the makes it seem as though the energy being referred to in this part of the  sentence is that of France.
    E    This construction is wordy and unclear; the referent of  it is ambiguous.
   

Grammatical  construction
    Implementing the equations has reduced sickness, sleeping on the job, and  fatigue; at the same time, it has increased efficiency. The three parallel  elements (have reduced x, y, and z) require and before the final element.
   
    A    The omission of and before  fatigue creates an unclear sentence.
    B     The omission of and before  fatigue creates an unclear sentence.
    C    Correct. The use of and in this  sentence unites the three parallel elements; the phrase while raising provides a clear contrast with have reduced.
    D    And is required to link the  parallel elements; the verb reduced applies to all  three parallel elements, so inserting lowered  before fatigue illogically suggests that fatigue actually increased.
    E    The insertion of was lowered destroys the parallel structure, and thus while raising has no logical referent here.