The best replacement for since is because.

The best alternatives to since are rated as following:
★★★★★  because
★★★★  sense
★★★★  as
★★★  for
★★  from
★★  ever since
★  because grammar
★  every since
★  after
★  established
★  for use
★  since then
★  before
  for exercises
  for grammar
  as grammar
  for worksheet
  hence
  while
  ago
  seeing as
  for exercise
  during
  make sense
  makes sense

Your alternative for since is not listed? Suggest!
Speaking about since, one probably shouldn't forget about past perfect.

Other search terms related to since and their ratings are:
★★★★★ past perfect
★★★★ comma
★★★ present perfect
★ past tense
past perfect continuous
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since
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