Answer: D. $146t$

Explanation:$1$. Find the mass of one object: Given that the total mass of $r$ identical objects is $t$ kilograms. Mass of one object = $\dfrac{\text{Total mass of r objects}}{\text{Number of objects}}$ Mass of one object = $\dfrac{t}{r}$ kilograms.

$2$. Calculate the total mass of $146r$ of these objects: Number of new objects = $146r$. Total mass of $146r$ objects = (Number of new objects) $\times$ (Mass of one object) Total mass = $146r \times \dfrac{t}{r}$

$3$. Simplify the expression: The $r$ in the numerator and the $r$ in the denominator cancel out (assuming $r \neq 0$, which is implied as $r$ is a number of objects). Total mass = $146t$ kilograms.

Alternative approach using proportionality: If $r$ objects have a mass of $t$. Then $1$ object has a mass of $\dfrac{t}{r}$. Then $146r$ objects have a mass of $146r \times \dfrac{t}{r} = 146t$.

Or, the number of objects is scaled by a factor of $\dfrac{146r}{r} = 146$. So the total mass will also be scaled by $146$. New total mass = $146 \times (\text{original total mass for r objects})$ New total mass = $146 \times t = 146t$.

$4$. Check the options: Option [D] is $146t$, which matches our result.

$5$. Conclusion: The expression representing the total mass of $146r$ objects is $146t$.