Can an oscillatory motion be non-periodic?

Which of the following relationships between the acceleration $a$ and the displacement $x$ of a particle involve simple harmonic motion?
$(a)\; a=0.7 x$
$(b)\; a=-200 x^{2}$
$(c)\; a=-10 x$
$(d)\; a=100 x^{3}$

On an average,a human heart is found to beat $75$ times in a minute. Calculate its frequency and period.

Define displacement variable and periodic function.

What is the angular frequency of a reference particle executing $SHM$?

$A$ particle executes simple harmonic motion according to the equation $x(t) = A \sin^2(\alpha t)$. If the time period of the $SHM$ is $0.2 \ s$, then the value of $\alpha$ (in units of $rad/s$) is (in $\pi$)