Solution

ID: past-exam-of-the-mathematics-course-of-the-university-of-cambridge/2003/iii/paper-17/4/c/solution

False even when both base and fibre are closed and oriented. Take the Hopf fibration , and define the smooth fiber bundle by . Its local trivializations are the Hopf trivializations times , and its fibre is .
The Künneth theorem for cohomology over a field says for these compact manifolds. Here it gives . If a symplectic form existed on this closed four-manifold, it would be exact, . Since ,
by Stokes theorem. But is a positive volume form in the symplectic orientation, so its integral is positive. This contradiction proves the claim fails. The mere bundle structure does not ensure that a fibrewise area class extends to the total space.

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