The libraries that build a new higher-level API for client-side programming is

Answer: Option B

Many web developers find it useful to build their web applications on top of a clientside framework library. These libraries are “frameworks” in the sense that they build a new higher-level API for client-side programming on top of the standard and proprietary APIs offered by web browsers: once you adopt a framework, your code needs to be written to use the APIs defined by that framework.