According to a recent report, glassworks constructed in the last twent

According to a recent report, glassworks constructed in the last twenty years had one-third the likelihood that they would produce noise levels above 100 decibels as glassworks built earlier.

A. had one-third the likelihood that they would produce noise levels above 100 decibels --- Had one third the likelihood is unidiomatic In addition, the comparison has gone awry. We must compare what the glassworks constructed in the past 20 years had ( meaning possessed, simple past ) with what the glassworks built earlier had.
“As glassworks built earlier” lacks a verb and is incorrect. It looks as if the recent works are acting the role of the earlier works

B. had one-third the likelihood of producing noise levels above 100 decibels--- the same problem as in A.

C. were one-third less likely to be producing noise levels above 100 decibels—‘less’ entails a ‘than’. The comparator is absent.

D. were one-third as likely that they would produce noise levels above 100 decibels –‘as likely that they would produce’ – is unidiomatic

E. were one-third as likely to produce noise levels above 100 decibels --- The best of the lot and the answer.