... in North American waterways less than a decade ago, zebra mussels have already earned a nasty reputation for their expensive habit of clogging water pipes in the Great Lakes area.
The first sighting
Although first sighted
Zebra mussels were first sighted
First sighting
Pembahasan: Adverbial Clause (Concession)
Karena sudah ada induk kalimat, tambahkan anak kalimat yang diawali konjungsi pertentangan although + S + P.
Bandingkan pilihanmu dengan sobat pembelajar yang lain.