企业用于研究开发的仪器和设备，单位价值在30万元以下的，可以采用加速折旧法计提折旧。( )

Only when their children leave home _________.

A．many parents did feel a sense of loss

B．did many parents feel a sense of loss

C．did feel many parents a sense of loss

D．do many parents feel a sense of loss