A small object, suspended by a string, rotates with constant speed, in a horizontal circle as shown in the figure. Point $O$ is at the centre of the circle. Neglect air drag. Which one of the following statement is correct?

In the figure shown the acceleration of $A$is,${\overrightarrow{a}}_A=15\hat{\mathrm{i}}+15\hat{\mathrm{j}}$ then the acceleration of $B$ is ($A$ remains in contact with $B$)

Block $B$ has a downward velocity in $m{s}^{-1}$ and given by $v_B=\frac{t^2}{2}+\frac{t^3}{6},$ where $t$ is in $s$. Acceleration of $A$ at $t=2 \mathrm{second}$ is 

If block $A$ is moving with an acceleration of $5{\mathrm{ms}}^{-2},$the acceleration of $B w.r.t.$ ground is 

In the figure acceleration of $A$ is $1{\mathrm{ms}}^{-2}$ upwards, acceleration of $B$is $7{\mathrm{ms}}^{-2}$ upward and acceleration of $C$ is $2{\mathrm{ms}}^{-2}$ upward. then acceleration of $D$ will be