English Education Vol. 05 No. 1. JANUARY 2017 72 The Students’ Ability in Differentiating Compound and Complex Sentences at Grade XI SMA Negeri 1 Angkola Selatan By: Rayendriani Fahemi Lubis, M.Ag., Yusni Sinaga, M.Hum., and Isma Yanti ABSTRAK Peneliti mengeksplorasi kemampuan siswa dalam membedakan kalimat majemuk dan kompleks. Tujuan dari penelitian ini adalah untuk menguji kemampuan siswa dalam membedakan senyawa dan kalimat kompleks pada kelas XI SMA Negeri 1 Angkola Selatan. Setelah menganalisis data, peneliti menemukan bahwa kemampuan siswa dalam membedakan kalimat majemuk dan kompleks pada kelas XI SMA Negeri 1 Angkola Selatan dapat dikategorikan cukup, dengan skor rata-rata 51,33 untuk kemampuan dalam kalimat majemuk dan 59,2 untuk kemampuan dalam kompleks. kalimat. Kemudian, berdasarkan data yang terkumpul, data telah dianalisis untuk membuktikan hipotesis dengan menggunakan rumus Z-Test. Hal ini dapat dilihat Z_ (hitung =) - 0,087 <Z_ (tabel =) 0,326 dengan tingkat signifikansi 0,05. Artinya hipotesis ditolak. Jadi, kemampuan siswa dalam membedakan kalimat majemuk dan kompleks adalah kemampuan yang cukup. Key words: Kalimat Majemuk dan Kalimat Kompleks A. INTRODUCTION English clearly stated in curriculum that the object of teaching learning process. It improves students’ skill in four skills of language. The language skill is the performance of speakers of a language in using their language as tool of communication in daily routine. It is the ability to use their language according to set of the conventional rules, they share among themselves. In teaching process, the students should be able to write sentences correctly. Sentence is not only the combination of some words but also have the elements. The elements can be subject (S), verb (V), object (O), or complement (C). The students need at least two elements to build sentences correctly. There are many factors of English that must be understood by students in the school to arrange a sentence such as vocabularies, tenses, and part of speech. The students must know the factors. Part of speech is one of the factors of mastery the sentence. There are eight parts of speech, they are noun, pronoun, verb, adjective, adverb, preposition,