In the following paragraph, which portion is the topic sentence?
Keeping a pet requires dedication and
selflessness; it is not a decision which should be
considered lightly, and one needs to take into
account all the responsibilities involved before
making the commitment. For example, fish tanks
need to be washed out on a weekly basis,
hamster cages need to be cleaned out regularly,
and dogs need to be walked daily. Moreover,
animals need constant love and affection, and
one's lifestyle will need to be adjusted when
accommodating a pet. Consequently, there are
many factors which need to be weighed up
before making such a commitment.