Discussion

Explanation:

Option 1, while partly true in itself is incomplete. Magnetic memory elements will have to become “sensitive enough to respond when the appropriate wires in the control matrix are switched on” but not so sensitive that “they respond when a neighbouring element is changed”.
Option 2, the thickness of aluminium oxide barriers is not a barrier since a working prototype has already been developed consisting “of a sandwich of two layers of magnetisable material separated by a barrier of aluminium oxide just four or five atoms thick”.
The passage mentions, “... magnetic memory elements will have to become far smaller and more reliable than current prototypes if they are to compete with electronic memory.”
Hence, the correct answer is option 3.

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