问题详情

GeorgesValensi"spatentlasteduntil1971because______.
A．nobodywouldofferanyrewardforhispatentpriortothattime
B．hispatentcouldnotbeputtouseforanunusuallylongtime
C．therewerenotenoughTVstationstoprovidecolorprograms
D．thecolorTVreceiverwasnotavailableuntilthattime.
请帮忙给出正确答案和分析，谢谢！