z 是实数当且仅当 =z 。https://gss3.bdstatic.com/-Po3dSag_xI4khGkpoWK1HF6hhy/baike/s=12/sign=e0d26234805494ee83220b1b2cf536f4/4afbfbedab64034f6bfc218da3c379310a551d03.jpg

There are many tips to decide whether a source is credible. Please select from the following examples the credible one. A: Publicly editable encyclopedias or “wikis” (e.g. Baidu Baike, Wikipedia) B: https://eric.ed.gov C: https:// emerald.edn.org D: ---