1. The problem asks to identify which diagram shows an enlargement of triangle U with a scale factor of 3 and the centre of enlargement at the cross. 2. The formula for enlargement with centre $O$ and scale factor $k$ is: If a point $P$ is enlarged to $P'$, then $$\overrightarrow{OP'} = k \times \overrightarrow{OP}$$ where $\overrightarrow{OP}$ is the vector from the centre of enlargement $O$ to the original point $P$. 3. To check each diagram, we verify if the enlarged triangle's vertices lie on lines through the centre of enlargement and original vertices, and if the distances from the centre to the enlarged vertices are exactly 3 times those from the centre to the original vertices. 4. Diagram A shows the enlarged triangle positioned such that each vertex lies on the line through the centre and the original vertex, and the distances are scaled by exactly 3. 5. Diagrams B, C, and D do not satisfy the scale factor of 3 correctly or the alignment with the centre. 6. Therefore, the correct diagram is A.