Susan is an adolescent client with pregnancy-induced hypertension (PIH). The physician orders 5% dextrose in Ringer’s solution and magnesium sulfate intravenously for her. Before the magnesium sulfate is administered, which of the following assessments would be the priority()

A. Maternal urinary output.

B. Fetal position.

C. Fetal heart rate variability.

D. Maternal respiratory rate.

对于受要约人延误的承诺，该承诺( )。

A．有效

B．无效

C．要约人未表示不接受有效

D．要约人虽表示接受也无效