1.Thereasonscanbelistedasfollows.Foronething…Foranother…
2.Whathascontributedtothisproblem?Inthefirstplace…Inthesecondplace…
3.Perhapsthemain/primary/mostimportantreasonis…
4.Itisnoeasytoidentifythereasonfor…whichinvolveseveralcomplicatedfactors.
5.Anumberoffactorscouldaccountfor/leadto/contributeto/resultin/beconductiveto…
6.Onemaytrace/attributethisproblemto…
7.Thisproblemmayresultfrom/largelydueto/stemfromacombinationoffactors.
8.Theexplanationforthisphenomenoninvolvesmanycomplexreasons…
9.Thereareavarietyofreasonsforthisphenomenon.
10.Therearethreereasonsforthis.