在网络体系结构中，传输层的主要功能是()
A
解析：传输层的主要功能是为端到端连接提供可靠的传输服务;为端到端连接提供流量控制、 差错控制、服务质量等管理服务。 路径选择发生在网络层， 数据格式变换与加密等发生在表示层， MAC 与 IP 地址映射发生在数据链路层。根据分析，选项 A 符合题意，故选择 A 选项。
Since we have a focused subject ，we should not talk ________.
It is important to ________ your skin from the harmful strong sunlight.
He drove fast and arrived an hour_____of schedule.
The girl who found the ring received a generous_____of five pounds.
We hoped to be able to move into our new house at the end of the month, but things didn ’t ______ as we expected.
Two-thirds of his property_____lost in the fire.
可累及心肌引发心肌炎的最常见病原体是（）
Decision on whether the message is right or wrong should at least come after _____what the message is.
5岁小儿的体重是（）
一胎龄35周早产儿，冬天出生，现年龄为1个月零2天。母乳喂养，体重已由出生时2.Okg增至3.Okg现首先应添加的辅食及其添加目的是（）