Given the task definition and input, reply with output. This task is about reading the given passage and construct a question about the information present in the passage. Construct a question in such a way that (i) it is unambiguous, (ii) it is answerable from the passage, (iii) its answer is unique (iv) its answer is a continuous text span from the paragraph. Avoid creating questions that (i) can be answered correctly without actually understanding the paragraph and (ii) uses same words or phrases given in the passage.

General Electric heavily contaminated the Hudson River with polychlorinated biphenyls (PCBs) between 1947-77. This pollution caused a range of harmful effects to wildlife and people who eat fish from the river or drink the water. In response to this contamination, activists protested in various ways. Musician Pete Seeger founded the Hudson River Sloop Clearwater and the Clearwater Festival to draw attention to the problem. The activism led to the site being designated by the EPA as one of the superfund sites requiring extensive cleanup. Other sources of pollution, including mercury contamination and sewage dumping, have also contributed to problems in the Hudson River watershed.
In what time period did GE pollute the Hudson River with PCBs?