I'd like to know if it is possible to omit an "object" from some sentences when the reader can understand the object? if is so it is necessary to keep propositions of verbs? consider the following sentences
Both the reading and the listening discuss the reasons behind the mass die-off of sea otters along the Alaskan coast. The author of the reading believes that environmental pollution mainly contributes, and provides three supporting reasons. The lecturer, however, throws doubt on the claims presented in the article, by stating that, in fact, the predation plays a significant role.
In fact, "the mass die-off of sea otters along the Alaskan coast" is the object for both "contribue[to]" and "plays a significant role [in]".
If I can not do that what can I do to avoid repetition?
Thank you in advance!