请问这个题为什么不能选 keep up?

keep up with 才可以，表示“保持、继续、坚持”。

ps：
keep up
To maintain in good condition:
保持良好状态：
kept up the property.
保存财产
To persevere in; carry on:
保持；继续：
We asked her to stop talking, but she kept up.
我们请她别再说话了，但她依旧说下去
To continue at the same level or pace.
并行：按相同的水平或步伐继续下去
To match one's competitors, colleagues, or neighbors in success or lifestyle:
不落后，赶得上：赶上对手、同事或邻居，指在成就或生活方式上：
unsuccessfully tried to keep up with his associates.
没能赶上他的同事们

如果要选keep up, 后面得接with,才表示继续，坚持，加油等

keep up 与keep on不同
keep up
v.
不低落, 维持, 继续
ps.keep up 是指雨，雪，好天气等持续不断

keep on
v.
继续, 穿着...不脱

表示“保持”时，keep on后面接动名词，keep up后面接名词

keep up with 是固定搭配，含有
跟上；不落后；赶上,符合题目的意思，你要选择keep up，但是缺with

得用with