answer: choose A.

this question examines the accuracy and instrument specifications of some measuring instruments, and examines the accuracy and rigor of thinking. The key to solving this problem is to record the reliable measurable values according to the accuracy of the instruments used. The accuracy of weighing substances with tray balance is 1.1g, and 11.7g of salt can be taken. The accuracy of measuring liquid volume by measuring cylinder is 1.1mL, so it is unreasonable to measure 21.48mL; There are 51mL, 111mL, 211mL, 251mL, 511m, 1111mL and so on in the specifications of the volumetric flask, but there is no 211mL; Neutralization titration should use burette, the accuracy of burette is 1.11mL, and the value of 18.21mL is reasonable.