关于代词和时态的问题（新概念四18课课文中的两个问题）Inanothergame,astheturtleswimsacrosstheoceanarium,thefirstporpoiseswoopsdownfromaboveandbuttshis(1)shellwithhis(2)belly.1.按理说第一个his指代tu

Question

关于代词和时态的问题（新概念四 18课课文中的两个问题）
In another game,as the turtle swims across the oceanarium,the first porpoise swoops down from above and butts his(1) shell with his(2) belly.
1.按理说第一个his指代turtle,第二个his指代porpoise,但是一句话中的两个his可以指代不同的事物吗?是不是原文不太严谨?
2.还有一个问题,此句话前面举的calf的一个例子用的是一般过去时,该句话也是举的例子为啥选用另一个时态(一般现在时).同样是例子为啥不统一时态.还是说其实没有那么讲究,大师用时态都比较随意?
附上第二段原文：
Whether it be bird,fish or beast,the porpoise is intrigued with anything that is alive.They are constantly after the turtles,the Ferdinands of marine life,who peacefully submit to all sorts of indignities.One young calf especially enjoyed raising a turtle to the surface with his snout and then shoving him across the tank like an aquaplane.Almost any day a young porpoise may be seen trying
to turn a 300-pound sea turtle over by sticking his snout under the edge of his shell and pushing up for dear life.This is not easy,and may require two porpoises working together.In another game,as the turtle swims across the oceanarium,the first porpoise swoops down from above and butts his shell with his belly.This knocks the turtle down several feet.He no sooner recovers his equilibrium than the next porpoise comes along and hits him another crack.

Answer 1

1.你说得没错,根据情况一句话中的两个代词确实指代不同的事物,但这不是绝对的,有的时候也可以指代同一个事物,看具体语境.
2.这里的时态其实过去时或者现在时都可以,所以不算错.除非有明显的时间标志或者其他体现,才局限于某种时态.