If open an existing file using the argument "a+", which one of the following is correct?

A、Whenitisopen,theoriginfilecontentremains,theaccessingpointermovestotheendofthefileandappending/readingoperationsareavailable.;
B、Whenitisopen,theoriginfilecontentremains,theaccessingpointermovestothebeginningofthefileandrewriting/readingoperationsareavailable.;
C、Whenitisopen,theoriginfilecontentisdeleted,onlyreadingoperationisavailable.;
D、Noneoftheaboveiscorrect.