“鸟类的黑手党”﹣﹣杜鹃,将自己的卵产到别的小鸟巢中,小鸟辛勤地为杜鹃孵卵并精心喂食杜鹃的雏鸟.对小鸟这种行为的解释,正确的是( ) ①是先天性行为 ②是学习行为 ③是由遗传因素决定的 ④是由环境因素决定的. A.①③ B.②④ C.①④ D.②③ 答案:AA new house ________ at the corner of the road and will be completed next month.A. is building B. been builtC. is being built D. be building