2 道大全的题不明白，求助

题一：According to interstudy, a nonprofit organization that studies health maintenance organizations (HMO'S ), they estimate that, in comparison to last year, when only 36% of the nation's 607 HOM's was profitable, this year 73% will be.

答案是：only 36% of the nation's 607 HOM'S were profitable last year; it estimates that this year 73% will be.

我不明白的是最后一个部分 it estimates that this year 73% will be 这个句子看起来很别扭，是正确的句子不？

题二：According to United States Air Force officials, a cannon shooting dead chickens at airplanes has proved helpful to demonstrate what kind of damage can result when jets fly to a flock of large birds.

答案是：that shoots dead checkens at airplanes has proved helful in demonstrating.

我选的是：shooting dead checkens at airplanes has proved helpful to demonstrate

我认为我选的也可以说得通，helpful to do 和helpful in doing 有什么区别吗？

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