a curved line used to sustain notes and make rhythm easier to read is called a
a curved line used to sustain notes and make rhythm easier to read is called a tie.
To get this answer, one can start by understanding the context of the question – in this case, the topic is related to music notation. Then, using a search engine or a music theory resource, one can search for terms related to notational symbols or markings that are used to indicate the prolongation of a single pitch. By browsing through the search results or relevant resources, one would come across the term "tie" which describes a curved line connecting two or more notes of the same pitch, indicating that they are to be played as a single sustained note. By reading and comprehending the information provided, one can conclude that a tie is the correct answer to the question.