$$\frac{3}{4}\tan^2 30° - \sec^2 45° + \sin^2 60° = \frac{3}{4}\times\frac{1}{3} - 2 + \frac{3}{4} = \frac{1}{4} - 2 + \frac{3}{4} = 1 - 2 = -1$$
Answer: (A) −1
Substitute standard values: $\tan 30° = \frac{1}{\sqrt{3}}$, so $\tan^2 30° = \frac{1}{3}$; $\sec 45° = \sqrt{2}$, so $\sec^2 45° = 2$; $\sin 60° = \frac{\sqrt{3}}{2}$, so $\sin^2 60° = \frac{3}{4}$. Then simplify step by step. Memorise Table 8.1 values — this type of substitution question is very common.