Is this sentence correctly using commas: polluted rivers, which can exist anywhere, are unsafe for swimming.

Which keywords and phrases in this author's purpose indicate that the author should use a descriptive essay structure? karen is writing about her experiences in researching the life of author charles dickens at british universities. she (speaks of) important and exciting discoveries, (such as) a previously unknown personal diary. she also (hopes to) cover other aspects of her experience; for instance, how other dickens scholars were (accommodating of) a new researcher—a rarity in some academic fields.