1. The problem asks to identify the type of differential equation given by $y' = \varphi(t)$. 2. This equation shows that the derivative of $y$ depends only on the variable $t$. 3. Such an equation is called an ordinary differential equation where the right side is a function solely of the independent variable $t$. 4. Among the options, the correct description is: "The right side function depends only on $t$ in terms of the derivative." 5. This matches option (a): "Баруун талын функц нь зөвхөн t-ээс хамаарсан уламжлалынхаа хувьд бодогдсон тэгшитгэл". 6. Therefore, the answer is option (a).