Can the words "of" and "if" ever be next to each other in a sentence? For example: "I was unsure of if I could complete the task." Is that correct, or should it be "I was unsure of whether I could complete the task?"
Also, in this sentence: "Scientists recently discovered that the disease is not harmful; it led to new approaches in scientific thinking ...." is the "it" an incorrect word? I had this, and the other question, on my SAT and I was just wondering. Thanks.