Answer: Syntax
Step-by-step explanation:
The options are:
a. Phonology
b. Morphology
c. Syntax
d. Semantics
• Phonology is how sound patterns are being studied.
• Morphology is how words are being studied and formed, and it also shows the relationship that exists between the words formed and other words. Here, word structure such as prefixes, suffixes and root words are analysed.
• Semantics is the meaning phrases and words.
• Syntax has to do with how words are arranged in order to form sentences.
Since it was reported that Koko can use 1000 different signs, and can understand 2000 words and that Koko is now creating statements by blending three to six words, the highest level that the animal may have attained is referred to as syntax.
Since according to the question, Koko can now use words to form sentences, it means Koko has attained syntax stage.