–Have you received Jack’s plan?

--Yes, but I don’t think his plan is _____.

A．worth being considered

B．worthy to be considered

C．worthy of considering

D．worth to be considered

以下物质：①金刚石 ②石油 ③干冰 ④一氧化碳 ⑤石墨

（1）可用于人工降雨的是______（填序号，下同）；

（2）可用来切割玻璃的是______；

（3）具有毒性的气体是______；

（4）具有还原性的固体单质是______．