在农作物管理中,下列措施可以提高净光合速率的是
①通风 ②增施有机肥 ③延长生育期 ④施NH4HCO3[ ]
A.①
B.①②③
C.①②④
D.①②
答案:C
Lucy , a _______ girl , helped the little boy find his parents. [ ]
A. twelve year old
B. twelve years old
C. twelve-year-old
D. twelve-years-old
线接触钢丝绳的股是由特制的异型钢丝绕制成股。