Thebasicunitinthestudyofmorphologyis______.

Thisisanimportantproblem_______toofewsocialscientistshaveresearched.

Acompoundisthecombinationofonlytwowords.

By"languageacquisitionisprimarilytheacquistionofthegrammaticalsystemoflanguage",linguistsmeanthat______.

Accordingtothe"principles-and-parameters"theory,"principles"refertohighlyabstractpropertiesofgrammarwhichareappliedtolanguageingeneralandwhichgeneratephrasesandatthesametimerestrainthepowerofMovea,while"parameters"allowgeneralprinciplestooperateincertainrestrictedways,accordingtowhichparticulargrammarsofnaturallanguagesvary.