请教GWD6-Q39的C选项

今天做了一套GWD，里面有个语法题不是很明白，

GWD6-Q39:

Twenty-two feet long and 10 feet in diameter,
the AM-1 is one of the many new satellites that is a part of 15 years effort
of subjecting the interactions of Earth’s atmosphere, oceans, and land surfaces
to detailed scrutiny from space.

1. satellites that is应该修饰satellites a
        part of 15 years effort of subjecting the interactions of Earth’s
        atmosphere, oceans, and land surfaces
2. satellites,
        which is同上 a part of a 15-year effort to
        subject how Earth’s atmosphere, oceans, and land surfaces interact
3. satellites,
        part of 15 years effort of subjecting how Earth’s atmosphere, oceans, and
        land surfaces are interacting
4. satellites that are part of an
        effort for 15 years意思变化 that has subjected the interactions
        of Earth’s atmosphere, oceans, and land surfaces
5. satellites
        that are part of a 15-year effort to subject the interactions of Earth’s
        atmosphere, ocean, and land surfaces

我觉得15 years effort足以排除了。。。

 (C)  satellites, part of 15 years effort of subjecting how Earth’s atmosphere, oceans, and land surfaces are interacting

如果subject 這邊為動詞, 那effort後面則需接to subject

插入how 也改變句意